The Human Heart

The Human Heart

    Heart is the wondrous pump that powers the human body. With each heartbeat, it sends life-giving blood throughout the body. Blood carries oxygen and food to all the body cells. The rhythmic beating of the heart begins about seven months before we are born. When the heart stops beating, we die unless a special device circulates and oxygenates our blood.

    The heart is a large, hollow, muscular organ divided into two pumps that lie side by side. Veins transport blood from throughout the body to the right-sided pump. That pump sends the blood to the lungs, where it picks up oxygen. The oxygenated blood then flows to the left side of the heart, which pumps it through arteries to the rest of the body. Valves control the flow of blood through the heart. The left-sided pump, which delivers blood throughout the body, is larger and stronger than the right pump.

    The nervous system regulates the heart and other parts of the circulatory system. A division of the nervous system, the autonomic nervous system, automatically controls the heart rate, increasing or decreasing it, depending on the body's needs. For example, the heart pumps slowly while a person sleeps, providing relatively small amounts of oxygen to the body. But the heart rate can be quickly speeded up and so increase the oxygen output enormously when a person exercises, becomes frightened, or needs to fight or run.

    Disease can strike any part of the heart. Disorders of the heart and blood vessels are the leading cause of death in the United States and many other countries. The most common heart disease affects the arteries that supply the heart muscle itself with blood. Disorders of those arteries usually develop over a person's lifetime. Deposits of fatty material block the arteries and so reduce the blood supply to the heart. If the heart muscle receives too little blood, it may work poorly or even die. Damage to the heart muscle resulting from a shortage of blood is called a heart attack. A mild heart attack may force a person to lead a less active life. A severe attack may make the heart unable to supply the body with enough blood even at rest and so cause a person's death. Disease may also strike other parts of the heart with equally destructive effects.

    Some of the most exciting advances in medicine have been in cardiology, the medical field that deals with diseases of the heart and blood vessels. For thousands of years, people with heart diseases did not even know they had such a problem. In the 1900's, doctors have learned to diagnose and treat certain heart conditions that once meant death. Discoveries of new drugs and the great progress in surgery have added years to the lives of many heart patients. Doctors have transplanted hearts and even developed machines that can temporarily do the work of the heart.

    Today, much research in cardiology focuses on learning about the causes of heart disease so that it can be prevented. Other research seeks to reduce death and disability from heart disease through the further development of new medicines and surgical techniques. For patients who have untreatable disorders, research continues into improving heart transplantation and producing an effective artificial heart.

    Interesting Facts About The Heart

The Human Heart is fully developed about eight weeks after
conception, when the embryo is only about 1 inch (2.5 centimeters) long. The heart begins to beat even earlier--four weeks after conception, when it is just a simple tube.
Ancient Egyptians believed that the heart was the center of the
emotions and the intellect. An illustration from the ancient
Egyptian Book of the Dead shows the god Anubis weighing a dead person's heart against a feather, the symbol of truth.
The Body's Entire Supply of Blood, about 5 quarts (4.7 liters), is
pumped through the body every minute. In one day, the heart pumps nearly 2,000 gallons (7,600 liters) of blood. In a 70-year lifetime, the heart pumps about 51 million gallons (193 million liters) of blood and beats 2 1/2 billion times.
Diseases of the Heart and Blood Vessels are the leading cause of death in the United States. More than twice as many people die from cardiovascular diseases as from all forms of cancer. More than half of these deaths are caused by heart attacks.
Heart Muscle differs in several ways from other muscles in the body. For instance, heart muscle has certain cells that act as "leaders." These cells contract and relax rhythmically, causing surrounding cells to do the same. Even when the leader cells are removed from the heart, they continue their rhythmic beat.
A Tireless, Powerful Muscle, the heart performs enough work in one hour to lift 3,000 pounds (1,400 kilograms)--roughly the weight of a small car--about 1 foot (30 centimeters) off the ground.

HEART TERMS

Angina Pectoris, is chest pain that occurs when the heart does not receive enough blood.

Angiography, is a technique used to X-ray blood vessels.

Angioplasty, is a technique used to clear arteries that have become blocked with fatty deposits.

Arrhythmia, pronounced uh RIHTH mee uh, is an abnormal heart rhythm.

Arteriosclerosis, is the hardening, thickening, and loss of elasticity in artery walls.

Atherosclerosis,is the formation of fat deposits on the inner lining of arteries.

Atrium, is either of the two upper chambers of the heart.

Cardiology, is the branch of medicine that deals with the diagnosis and treatment of disorders of the heart.

Coronary Arteries are the vessels that supply oxygen-rich blood to the heart muscle itself.

Coronary Artery Disease (CAD) is the narrowing of the arteries that supply blood to the heart, reducing the amount of blood the heart muscle receives.

Coronary Bypass is a type of surgery used to rechannel blood flow past blocked coronary arteries.

Diastole, pronounced dy AS tuh lee, is the period of heart activity when the ventricles relax.

Electrocardiograph (ECG) is an instrument used to detect heart damage or diagnose heart disorders.

Heart Attack is a sudden and complete blockage of a coronary artery, stopping blood flow to one section of heart muscle.

Heart Failure occurs when the heart fails to pump enough blood.

Systole, is the period of heart activity when the ventricles contract.

Ventricle, is either of the two lower chambers of the heart.

The structure of the heart

    Each person's heart is about the size of the person's fist. A newborn baby's heart weighs about 2/3 ounce (19 grams). An adult's heart weighs from 9 to 11 ounces (255 to 312 grams). The heart lies near the middle of the chest, between the lungs. The heart lies closer to the front of the chest than to the back and slightly to the left side.

    Muscular walls. The heart consists chiefly of muscle. Heart muscle, also called myocardium or cardiac muscle, forms the walls of the heart as well as the septum, a wall that divides the left and right sides of the heart. All the muscles contract and relax, thereby pushing blood through the heart.

    A membrane called the epicardium covers the outer surface of the heart. Another membrane, the pericardium, surrounds the epicardium. It completely encloses the heart and extends above the blood vessels that emerge from the top of the heart. A slippery fluid between the epicardium and the pericardium enables the heart to contract smoothly.

    Heart muscle differs from the other muscles of the body--skeletal and smooth muscles. Skeletal muscles, such as those in the arms and legs, have long fibers with alternate dark and light bands called striations. We can consciously control the skeletal muscles. Smooth muscles form the walls of the stomach, intestines, and most other internal organs. The muscles lack striations, and we do not consciously control them. They work automatically. Heart muscle has striations like skeletal muscle. But it contracts and relaxes automatically like smooth muscle. In addition, heart muscle cells act as one cell. When one heart muscle cell contracts or relaxes, the cells around it do the same. For that reason, the heart beats continuously and rhythmically throughout a person's life.

    Chambers. The septum divides the heart lengthwise, and valves divide it crosswise. Each side of the heart thus has two chambers, one above the other. A thin membrane called the endocardium lines each chamber. The top chambers, called the right atrium and left atrium, receive and collect blood returning to the heart through the veins. After the atria (plural of atrium) have filled with blood, they contract and squeeze blood into the lower chambers, called the right ventricle and left ventricle. After the ventricles have filled, they contract and pump blood out of the heart through the arteries. The ventricles have extremely thick walls. The ventricles, which must squeeze blood from the heart, are much larger and stronger than the atria.

    Blood vessels. Blood enters and leaves the heart through several major vessels. Blood from the body flows into the right atrium through the body's two largest veins. The superior vena cava brings blood from the head and arms. The inferior vena cava carries blood from the trunk and legs. Other blood vessels transport blood between the heart and lungs. Pulmonary veins return blood from the lungs to the left atrium. The pulmonary artery carries blood from the right ventricle to the lungs. The aorta is the largest artery. It receives oxygenated blood from the left ventricle and, through numerous branches, distributes it throughout the body. The pulmonary artery and the aorta are sometimes called the great vessels.

    The first arteries that branch from the aorta are the two major coronary arteries. They bring blood to the heart and so enable it to continue pumping. These two coronary arteries divide into many branches as they cover the heart. Diseases that affect the coronary arteries are among the most serious problems cardiologists treat because the arteries nourish the heart muscle itself.

    Valves regulate the flow of blood through the heart. The valves have flaps that open as blood pours from a chamber. When the flaps close, they prevent blood from flowing back into the chamber. Two valves separate the atria and the ventricles. They are called the atrioventricular valves or AV valves. The AV valve between the right atrium and right ventricle has three flaps and is called the tricuspid valve. The AV valve on the left side of the heart has two flaps and is called the mitral valve. The heart also has a valve, called a semilunar valve, between each ventricle and its great vessel--the pulmonary artery or the aorta. Each semilunar valve has three flaps shaped like half moons. When the right ventricle contracts, it delivers blood to the pulmonary artery. The semilunar valve that controls the blood flow to the pulmonary artery is known as the pulmonic valve. The left ventricle squeezes blood into the aorta. The semilunar valve on the left side is called the aortic valve.

The work of the heart

    Pumping blood to the lungs. Blood from the body that enters the right side of the heart contains carbon dioxide, a gaseous waste the cells produce in creating energy. Blood enters the right atrium through the superior vena cava and inferior vena cava. The atrium fills with blood and then contracts, squeezing the blood through the tricuspid valve into the right ventricle. After the ventricle is filled, pressure forces the tricuspid valve to close and the pulmonic valve, leading to the pulmonary artery, to open. The ventricle contracts, and the blood gushes through the pulmonary artery and into the lungs. In the lungs, carbon dioxide is removed from the blood and oxygen is added. The oxygenated blood then flows through the pulmonary veins to the left side of the heart.

    Pumping blood throughout the body. Oxygenated blood from the lungs enters and fills the left atrium. The atrium then contracts, which squeezes the blood through the mitral valve into the left ventricle. After blood fills the ventricle, the mitral valve closes and the aortic valve opens. Blood pours into the aorta and flows through arteries to the body tissues.

    Regulating the heart rate. Both sides of the heart pump blood at the same time. As the right ventricle contracts and sends blood to the lungs, the left ventricle contracts and squeezes blood out to the body. The heart's cycle of activity has two periods, systole and diastole. Systole occurs when the ventricles contract, and diastole when they relax. One complete contraction and relaxation of the heart muscle makes up one heartbeat.

    The contraction and relaxation of the ventricles also open and close the heart valves. Closing of the valves produces the "lub dub" sound of the heartbeat, which doctors can hear with an instrument called a stethoscope. As the ventricles contract, the mitral and tricuspid valves close, causing the first sound of a heartbeat. Immediately after the valves close, pressure in the ventricles forces the aortic and pulmonic valves to open. After the contraction ends, pressure in the ventricle drops. The aortic and pulmonic valves then close, causing the second heart sound. The pressure in the atria is then greater than in the ventricles, and so the tricuspid and mitral valves open and blood begins to fill the ventricles again.

    The autonomic nervous system controls the heart rate. Special cells send electrical impulses (nerve signals) through the heart, causing it to contract and relax rhythmically. The impulse begins in a small bundle of muscle fibers called the sinoatrial node, or S-A node. The S-A node is often called the pacemaker of the heart because it sets the pace of the heartbeat as it sends out rhythmic signals. The S-A node lies in the right atrium near where the superior vena cava enters the heart. The S-A node sends impulses along certain pathways, causing the atria to contract when the electrical signal reaches them. The impulse then arrives at another node, called the atrioventricular node, or A-V node. The A-V node lies between the atria and ventricles. It delays the nerve signal briefly, allowing the ventricles enough time to fill with blood. As the impulse continues, the ventricles contract.

    The nerves of the autonomic nervous system control the S-A and A-V nodes. Stimulation of those nerves can quicken or slow the heartbeat. When the body needs more blood, as during vigorous exercise, the nervous system stimulates the S-A node, which increases the rate of its impulses. The impulses keep the heart chambers contracting at a faster speed, thus pumping more blood.

    A person's size largely determines a person's resting heart rate. The bigger a person is, the slower the heart rate. A newborn baby's heart beats about 120 times per minute. The typical rate for adults is 72 beats per minute. But doctors consider resting rates from 60 to 100 beats per minute within the normal range. Athletic training enlarges the heart and slows the heartbeat. Many well-trained athletes have resting rates from 40 to 60 beats per minute.

    Regulating blood pressure. Blood in the circulatory system, like water in the pipes of a water system, is always under pressure. Blood pressure refers to the force with which the blood pushes against the walls of the arteries. That force drives blood from the heart to all parts of the body. Each person's blood pressure reflects the amount of blood in the body, the strength and rate of the heart's contractions, and the elasticity of the arteries. Because the heart pumps in cycles, pressure in the arteries rises and falls during systole and diastole. Contraction of the heart produces systolic blood pressure, and relaxation produces diastolic blood pressure.

    The heart helps regulate blood pressure by producing a hormone that aids the kidneys in eliminating salt from the body. Excess salt may contribute to high blood pressure, a condition doctors call hypertension. Hypertension can injure the heart, brain, and kidneys. Over many years, it can damage arteries and lead to heart disease.

Coronary artery disease

    Disease can strike any part of the heart. However, the term heart disease usually means coronary artery disease (CAD), the most common form of heart disease. The condition affects the blood vessels that nourish the heart itself. CAD narrows the coronary arteries and so reduces the blood supply to the heart.

    About 5 per cent of the blood pumped from the heart goes directly to the coronary arteries. The blood carries the oxygen and dissolved nutrients (foods) the heart needs to do its work. The heart can store most nutrients. But it cannot store oxygen and needs a constant supply. Coronary artery disease may affect the heart's ability to pump by reducing or stopping the oxygen supply.

    Some people with CAD suffer severe pain. Others feel no pain and do not even know they have a heart problem. If the disease worsens, a heart attack may result. A heart attack damages the heart muscle or may even cause sudden death. Most cases of CAD can be treated, but the disease should be diagnosed (identified) as soon as possible.

    Risk factors. Cardiologists cannot say for certain who will be stricken with coronary artery disease. However, medical research shows that certain conditions and habits may lead to the disease. Doctors call those conditions and habits risk factors. Some risk factors fall beyond a person's control. For example, CAD strikes more men than women and older people more than younger ones. In addition, the disease may run in a person's family.

    Several other risk factors involved in coronary artery disease can be controlled. The most important risk factor is the amount in the blood of a fatty substance called cholesterol. The higher a person's cholesterol level is, the more likely coronary artery disease will strike because the fatty deposits narrow the blood vessels. People can control the blood cholesterol level by reducing the amount of cholesterol and animal fats in the diet. See CHOLESTEROL.

    Other controllable risk factors that may cause coronary artery disease include high blood pressure and cigarette smoking. High blood pressure forces the heart to work harder, which may bring on a heart attack. People can lower their blood pressure by losing weight, exercising, and eating less salt. Certain medicines also help reduce high blood pressure. Cigarette smokers are more likely to have CAD than nonsmokers. Heavy smokers run more than twice the risk of a heart attack than nonsmokers. But smokers who quit significantly reduce the risk of heart disease. Other risk factors that may contribute to the development of coronary artery disease include diabetes, extreme fatness, and stress.

    Regular physical examinations often reveal the development of controllable risk factors. Doctors may then advise patients to quit smoking or to follow a specific diet to control high blood pressure, the cholesterol level, or weight.

    Causes. Nearly all coronary artery disease results from arteriosclerosis--a hardening, thickening, and loss of elasticity of the artery walls. In most cases, the inner layer of the artery wall becomes damaged, causing a form of arteriosclerosis called atherosclerosis. The inner walls of healthy arteries are smooth, and so blood flows easily. But in atherosclerosis, deposits of fats and calcium build up on the inner walls, hampering the blood flow through the artery. The fat and calcium deposits are called plaques.

    Plaques can completely block an artery and stop the blood flow. In addition, they can narrow an artery and so reduce blood flow enough to form a thrombus (blood clot). Plaques often crack, releasing substances that also can lead to blood clots. If a blood clot blocks a coronary artery, it causes a heart attack. A blood clot that occurs in an artery in the brain causes a stroke.

    Symptoms and diagnosis. Coronary atherosclerosis usually takes many years to develop. Doctors have found coronary artery plaques in young soldiers killed in battle. But symptoms seldom occur until age 50 or later. In some cases, the first symptom is a heart attack or sudden death. However, a typical early symptom may be pain in the chest from exercising or some other activity that makes the heart work harder than usual. Doctors call such pain angina pectoris, or simply angina. The narrowed coronary arteries supply the heart with less oxygen, which may cause pain when the heart must work harder. After the exercising or other activity is stopped, the pain usually disappears. However, angina may worsen if left untreated. Patients may then suffer from frequent attacks, even when resting.

    Physicians diagnose coronary artery disease by first listening to their patients tell of their general physical condition and past illnesses. They note any history of angina or heart attack and the presence of any risk factors. Physical examination may reveal other risk factors, such as high blood pressure or heart damage.

    Doctors use an instrument called an electrocardiograph to detect heart damage or disturbances of the heart rhythm. The instrument produces a record called an electrocardiogram (ECG), which displays the electrical activity of the heart muscle. The impulses are printed on moving paper that shows the heart's electrical activity as a series of wavy lines. Major waves represent contraction of the ventricles. Minor waves represent relaxation of the ventricles and contraction and relaxation of the atria. Most ECG's are taken with the patient lying down. But many physicians take a patient's ECG during exercise. Such a stress ECG shows whether a patient's heart--even if the patient has no chest pain--receives enough oxygen during vigorous exercise.

    Doctors also use a method called radionuclide imaging to detect CAD. A doctor injects a radioactive element into a patient's bloodstream. The doctor can view the element on a screen as it spreads into the heart muscle. Areas that do not receive blood appear blank on the image. Doctors generally use radionuclide imaging with a stress ECG.

    If the usual diagnostic techniques leave doubt, physicians may perform cardiac catheterization followed by coronary angiography. They insert a long, flexible tube called a catheter through a large blood vessel, usually an artery in the area where the thigh and abdomen meet. They push the catheter up to where the coronary arteries begin and inject dye. The inside of the arteries can then be viewed and recorded on X-ray film called an angiogram. The test clearly shows the condition of the coronary arteries. Coronary angiography presents a small risk of injury or even death. Doctors therefore perform it only in difficult diagnostic cases.

    Treatment. Doctors cannot cure coronary artery disease. In some cases, they advise patients to change their life style to help slow the development of CAD. Victims can be treated with drugs or surgery to help them live a normal life. Doctors evaluate each patient with CAD to determine which treatment would provide the greatest benefit.

    Physicians prescribe various drugs to treat different symptoms of CAD. Several drugs relieve angina. For example, nitroglycerin tablets placed under the tongue enlarge the coronary arteries, enabling more blood to flow past the fatty deposits. Nitroglycerin can stop angina pain within two minutes. Beta-blockers and calcium blockers may prevent angina. Beta-blockers slow the action of the heart and reduce its contracting force. The heart's demand for oxygen then decreases, making it easier for the heart to pump. Calcium blockers work like beta-blockers on the heart and also relax the coronary arteries. The two drugs also relieve high blood pressure. The drug digitalis strengthens the action of weak hearts. Many doctors advise coronary artery disease patients to take one aspirin tablet a day. Aspirin thins the blood and can help prevent blood clots in the coronary arteries.

    If drugs fail to control coronary artery disease, doctors consider other techniques to correct the problem. In the easiest technique, coronary angioplasty or simply angioplasty, doctors insert a catheter with a deflated balloon attached into the narrowed area of the coronary artery. They then inflate the balloon, which pushes the blockage aside and enlarges the artery. Angioplasty works in about 85 per cent of patients at first. But in about a third of those patients, blockage returns within three months. For some patients, various methods may prolong the benefits of angioplasty. For example, intense beams of light from devices called lasers burn away new plaque deposits. Or the placement of tiny metal props in the artery may keep it open.

    Should catheter methods fail, most cardiologists suggest coronary artery bypass graft surgery. In bypass surgery, doctors first remove a short piece of a blood vessel, usually a vein from the patient's leg or from an artery in the chest. They attach one end of the vessel to the aorta and the other end to the affected coronary artery, bypassing the blocked section. Surgeons can stop the heart to perform a bypass by using a heart-lung machine. The device has an electric pump and a system of membranes that do the work of the heart and lungs. The machine removes carbon dioxide from the blood and delivers oxygenated blood to the body tissues. A coronary bypass can ease symptoms of angina and prolong the lives of patients with more severe CAD. But it does not stop atherosclerosis.

Heart attack

    Almost all heart attacks occur when a blood clot suddenly and completely blocks a coronary artery. The condition is called a coronary thrombosis, or simply a coronary. The heart muscle supplied by the blocked artery becomes damaged because it receives too little oxygen. Unless blood flow returns within minutes, muscle damage increases. The heart cells begin to die after four to six hours without blood. The damage can affect the heart's ability to pump and cause the death of the victim. The body reacts to a heart attack with its own defenses. Substances in the blood can dissolve clots and permit blood to flow freely again. If the clot is dissolved within four to six hours of the attack, the heart suffers less damage.

    Symptoms. Before having a heart attack, many people suffer from angina, feel dizzy, have indigestion, or experience other symptoms. Some people have no warning signs. Most heart attacks cause severe pain. Victims describe the pain as a dull, crushing ache in the chest, but it may extend into the neck, jaw, arms, or back. The pain may last from a few minutes to several hours.

    A person who has chest pain and suspects it may mean a heart attack should seek medical help immediately. Some victims may stop breathing, and their heart may stop beating. A first-aid technique called cardiopulmonary resuscitation (CPR) can maintain a person's breathing and circulation until medical help arrives and the victim is taken to a hospital. But cardiopulmonary resuscitation should be performed only by someone trained in the technique.

   Diagnosis and treatment. Soon after a heart attack victim reaches the hospital, doctors use an ECG to make sure the patient actually had a heart attack and not chest pain resulting from some other disorder. Injured heart muscle causes abnormal ECG waves. Doctors also use certain blood tests to detect a heart attack. But the tests are not useful until six hours after the attack.

    If a victim still has pain, doctors may administer a painkilling drug, such as morphine. They also use drugs to dissolve clots in the blocked artery. If the drugs fail to dissolve the clots, doctors may perform emergency angioplasty or bypass surgery.

    After being hospitalized, heart attack patients are monitored for complications in the intensive care unit. Two major complications are heart failure and arrhythmia. Heart failure occurs if the heart does not pump enough blood because of extensive damage to the heart muscle. In most cases, heart failure can be successfully treated. In arrhythmia, the heart's electrical system produces an abnormal rhythm. One kind of arrhythmia, ventricular fibrillation, occurs when electrical signals in the ventricles fire randomly. Ineffective heart rhythm and sudden death may result from ventricular fibrillation. Arrhythmias can be readily treated under medical care.

    The death rate among heart attack victims who do not get medical care is more than 20 percent. Some of them die before reaching a doctor. Other victims ignore their symptoms. The death rate among hospitalized patients ranges from 5 to 10 percent. Heart attack patients with repeated chest pain, arrhythmias, or heart failure have a greater risk of another attack than do patients without those problems.

History of heart research

    Early beliefs about the heart. In ancient times, many people believed that the heart had special importance. For example, the Chinese thought that each emotion originated in a certain organ and that happiness dwelt in the heart. Chinese physicians diagnosed many illnesses and prescribed treatment by taking the pulse at the wrist. The ancient Egyptians considered the heart to be the source of intelligence and emotion.

    The ancient Greeks learned from battlefield injuries and animal sacrifices that the heart was a beating organ. In the A.D. 100's, the Greek physician Galen developed the first medical theories based on scientific experiments. Galen observed the heartbeat and realized that the heart put blood in motion. But he thought that the heart's right ventricle forced blood into the left ventricle through holes in the septum. Galen also believed that the liver converted food into blood, which then flowed through the body and was used up.

   Discovery of circulation. Doctors accepted Galen's theories--in spite of the many errors--until the 1500's. In the mid-1500's, a Flemish-born physician named Andreas Vesalius described veins and arteries. He also showed that no holes exist between the heart's chambers. Also in the 1500's, Michael Servetus, a Spanish physician and theologian, reasoned that blood flows between the heart and lungs. But his studies were not publicized because of his unpopular religious beliefs.

    The theory of blood circulation was first published in 1628, by William Harvey, an English physician. His work became the basis of modern research on the heart and blood vessels. Harvey showed that the heart works like a pump. He described how blood flows from the heart to the lungs, back to the heart, out to the body, and back to the heart. Harvey believed that small blood vessels called capillaries connect arteries and veins. The idea of capillaries had been proposed in the 1500's by an Italian anatomist named Andrea Cesalpino. Marcello Malpighi, an Italian physician, proved their existence in 1661. In the early 1700's, Stephen Hales, an English clergyman and scientist, became the first person to measure blood pressure. He placed a glass tube in a horse's artery after breaking through the animal's skin. Hales published the result of this experiment in 1733.

    Invention of new medical instruments. During the 1800's, many inventions expanded doctors' knowledge of the heart and helped in their diagnosis and treatment of heart problems. In 1816, a French physician named Rene Laennec invented the stethoscope, which enabled doctors to listen to sounds of the heart and other organs. In 1880, Samuel Siegfried von Basch, a Viennese physician, developed the sphygmomanometer, an instrument to measure blood pressure without breaking the skin. Russian physician Nikolai Korotkoff used a stethoscope in 1905 to take the pulse while measuring blood pressure, thus recording systolic and diastolic blood pressure. Doctors still use this technique.

    In 1903, Willem Einthoven, a Dutch physiologist, invented the string galvanometer, a device to measure minute electrical currents generated by the activity of the heart, and so developed the basis of the electrocardiograph. By the 1920's, the electrocardiograph had become the chief diagnostic tool in cardiology.

    Development of heart surgery. An American cardiologist named James B. Herrick made the first diagnosis of a heart attack in 1912. In 1938, Robert E. Gross, an American surgeon, performed the first successful repair of a congenital heart defect. Gross sewed the hole in the artery of a child suffering from patent ductus arteriosus. In 1944, Helen Brooke Taussig and Alfred Blalock, two American physicians, developed an operation to help correct abnormal circulation of blue babies.

    In 1952, American surgeon Charles Hufnagel operated on a beating heart and implanted the first artificial heart valve. In 1953, another American surgeon, John H. Gibbon, and his associates successfully used a heart-lung machine they developed, which enabled doctors to stop the heart while the device pumped and oxygenated the blood. Doctors could then repair defects that could not be corrected while the heart beat.

    F. Mason Sones, Jr., an American surgeon, performed the first angiography in 1958 and gained the first view of blockages caused by CAD. The coronary bypass operation was perfected in the late 1960's by Rene Favaloro, an Argentine physician working in the United States. In 1967, American surgeons Michael DeBakey and Adrian Kantrowitz successfully implanted the first assisting heart. This device temporarily helped a diseased or overworked left ventricle.

    The first heart transplants and artificial hearts. A team of South African surgeons headed by Christiaan Barnard performed the first human heart transplant in 1967. The patient lived 18 days and died of a lung infection. Norman Shumway pioneered in heart transplants in the United States. He and his surgical team performed the first U.S. heart transplant on an adult patient in 1968. Shumway refined transplant techniques and performed more transplants than any other surgeon.

    In the late 1960's and early 1970's, doctors performed many heart transplants. But most patients died within a year, mainly because the body rejected the new organ. Doctors almost stopped doing heart transplants. Then in the 1980's, they began using a drug called cyclosporine to fight rejection. Cyclosporine greatly increased the survival rate among transplant patients. The shortage of donor hearts has become the chief obstacle to successful heart transplants today.

    In 1982, an American surgical team headed by William DeVries implanted the first permanent artificial heart in a human patient. Robert Jarvik, an American physician, designed the device. The patient, Barney Clark, suffered from many medical complications and died 112 days later. A number of other patients received the Jarvik heart, but none of them survived two years. In 1990, the U.S. Food and Drug Administration withdrew approval of the Jarvik device. Another model, similar to the Jarvik, is used as a temporary replacement heart at a few medical centers in the United States.

    Progress in treatment and prevention occurred about the same time as the dramatic advances in heart surgery. In the late 1960's, researchers developed beta-blockers. These drugs help in reducing high blood pressure, preventing angina, and controlling certain arrhythmias. Calcium blockers, which work like beta-blockers, appeared in the 1970's.

    In 1977, a Swiss physician named Andreas Gruentzig performed the first angioplasty, a nonsurgical procedure to open a blocked artery. Researchers also developed various techniques to use with angioplasty to prolong its effectiveness. The first implantable defibrillator became available in 1985. The device senses excessive contractions of the ventricles and sends a small electrical shock to stop them.

    Meanwhile, prevention of heart disease has centered on eliminating controllable risk factors. High blood pressure, high blood cholesterol, and cigarette smoking are major causes of CAD. Removal of those risk factors may prevent the development of the disease.

    Much of what has been learned about preventing heart disease comes from extensive medical research. For example, the Framingham Heart Study has provided considerable knowledge about the risk factors involved in coronary artery disease. The study began in 1948 in Framingham, Mass., and has examined the functioning of the heart in more than 5,000 people. Such research has led scientists to develop new drugs to treat high blood pressure and high cholesterol.

    Many people have improved the condition of their heart by learning the value of preventive medicine. For example, they have their blood pressure and cholesterol level checked regularly. Many people with mild high blood pressure have reduced it by limiting the salt and calorie content of their diet. Others have lowered their cholesterol level by watching the amount of cholesterol, saturated fat, and calories in their diet. In addition, more and more people exercise regularly, which helps keep body weight down and so helps lower cholesterol and blood pressure.