heart-lung machine, device that maintains the circulation of the blood and the oxygen content of the body when connected with the arteriovenous system; it is also called the pump oxygenator. The machine is used in open-heart surgery when it is necessary to effect a bypass of the circulatory system of the heart and lungs. The oxygenator repeatedly draws off the blood from the veins, reoxygenates it, and pumps it into the arterial system. The contractions of the heart are halted by running a potassium citrate solution through the coronary vessels. The surgeon is thus enabled to open the heart and make the necessary repairs while the heart is still and his view is not obstructed by blood.

heart, artificial, external or surgically implanted mechanical device designed to replace a patient's diseased heart. The first one used on a human being, the Jarvik-7, was implanted (1982) in Barney Clark, who lived for 112 days; another patient, William Schroeder, lived 620 days. Two major drawbacks of the Jarvik-7 were the danger of stroke from clots formed in the artificial heart and the need for the patient to be hooked to the external air compressor that powered the pump. By 1989 such devices had largely become a bridge to human heart transplants (see transplantation, medical).

Beginning 2001, however, a second type of artificial heart, the AbioCor, was implanted in a number of patients. Unlike the Jarvik-7, the AbioCor is powered by electrical energy that is transmitted from a battery across the skin to an internal coil and backup battery. Because an opening in the skin is not needed to allow passage for tubes or wires, the risk of infection is greatly reduced. In addition, the external battery pack is designed to worn on a belt or suspenders, enabling the patient to be mobile. On average, the patients who received the heart from 2001 to 2004 and survived the operation lived for five months; the longest lived not quite 17 months. In 2006 the AbioCor was approved for use in patients who do not qualify for a heart transplant if their life expectancy as a result of heart failure is less than month; the device is also approved as a temporary measure for patients awaiting a transplant.

A related device, the ventricular assist device (VAD), or "artificial ventricle," is an internally implanted pump designed to aid a person with a failing left ventricle; unlike an artificial heart, it does not require removal of the patient's heart. A version for temporary use was developed in 1964. In 1991 doctors implanted the first portable VAD; it was powered by a battery pack. Its pump used a special interior lining to promote the growth of a surface similar to that which lines the blood vessels, reducing the risk of the formation of blood clots, which can cause stroke.

heart disease, any of several abnormalities of the heart and its function in maintaining blood circulation. Heart disease is the cause of approximately half the deaths in the United States each year. Among the most common causes of heart disease are degenerative changes in the coronary blood vessels, infectious diseases, and congenital heart disease. Congenital defects result from abnormal development of the fetal heart, commonly in the valves or septa. Such defects can be precipitated by environmental conditions in the uterus, such as the presence of the rubella virus, or they can be inherited. Infectious diseases acquired after birth, such as rheumatic fever, syphilis, and endocarditis, can also damage the valves of the heart. In addition, the heart muscle itself can be affected: hypertensive heart disease (see hypertension) can cause it to enlarge, and it can become inflamed by rheumatic fever. Arteriosclerotic depositions in the coronary arteries result in the narrowing of these vessels, causing insufficient blood flow and oxygen to the heart muscle, a condition known as coronary artery disease. The characteristic radiating chest pain, angina pectoris, is the most prominent symptom of this condition. Coronary arteries already narrowed by arteriosclerosis are made susceptible to blockage by a clot (coronary thrombosis), causing the death of the heart muscle supplied by the affected artery, a life-threatening event called a myocardial infarction, or heart attack. Hypertensive, coronary, congenital, and other forms of cardiovascular disease, either singly or in combination, can lead to a state in which the heart is unable to expel sufficient blood for the metabolic demands of the body, ultimately resulting in congestive heart failure. Disturbances in the normal heartbeat, called arrhythmias, can occur by themselves or in conjunction with other heart problems, for example infarction affecting the area of the heart that controls the heartbeat.

heart attack: see under infarction.

heart, muscular organ that pumps blood to all parts of the body. The rhythmic beating of the heart is a ceaseless activity, lasting from before birth to the end of life.

Anatomy and Function

The human heart is a pear-shaped structure about the size of a fist. It lies obliquely within the chest cavity just left of center, with the apex pointing downward. The heart is constructed of a special kind of muscle called myocardium or cardiac muscle, and is enclosed in a double-layered, membranous sac known as the pericardium. A wall of muscle divides the heart into two cavities: the left cavity pumps blood throughout the body, while the right cavity pumps blood only through the lungs. Each cavity is in turn divided into two chambers, the upper ones called atria, the lower ones ventricles. Venous blood from the body, containing large amounts of carbon dioxide, returns to the right atrium. It enters the right ventricle, which contracts, pumping blood through the pulmonary artery to the lungs. Oxygenated blood returns from the lungs to the left atrium and enters the left ventricle, which contracts, forcing the blood into the aorta, from which it is distributed throughout the body. In addition, the heart employs a separate vascular system to obtain blood for its own nourishment. Two major coronary arteries regulate this blood supply.

Cardiac Cycle

Blood flows through the heart in one direction only. It is prevented from backing up by a series of valves at various openings: the tricuspid valve between the right atrium and right ventricle; the bicuspid, or mitral, valve between the left atrium and left ventricle; and the semilunar valves in the aorta and the pulmonary artery. Each heartbeat, or cardiac cycle, is divided into two phases. In the first phase, a short period of ventricular contraction known as the systole, the tricuspid and mitral valves snap shut, producing the familiar "lub" sound heard in the physician's stethoscope. In the second phase, a slightly longer period of ventricular relaxation known as the diastole, the pulmonary and aortic valves close up, producing the characteristic "dub" sound. Both sides of the heart contract, empty, relax, and fill simultaneously; therefore, only one systole and one diastole are felt. The normal heart has a rate of 72 beats per minute, but in infants the rate may be as high as 120 beats, and in children about 90 beats, per minute. Each heartbeat is stimulated by an electrical impulse that originates in a small strip of heart tissue known as the sinoatrial (S-A) node, or pacemaker.

Advances in Cardiology

One of the important advances in cardiology is the artificial pacemaker used to electrically initiate a normal heartbeat when the patient's own pacemaker is defective (see arrhythmia); it may be surgically implanted in the patient's body. Similarly, an internal defibrillator may be implanted to deliver an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances. Another familiar tool of the cardiologist is the electrocardiograph (EKG), which is used to detect abnormalities that are not evident from a physical examination (see electrocardiography).

One of the most important advances in heart surgery during the 1960s was the transplantation of the healthy heart immediately after the death of an individual (the donor) to a recipient suffering from incurable heart disease (see transplantation, medical). In the 1980s new advances in the design and construction of an artificial heart—both the entire organ and such parts as the valves and large blood vessels—showed some promise in treating cardiovascular disease (see heart, artificial), but the limited success that has characterized artificial heart implantation thus far has led many experts to question the efficacy of such measures. Although the artificial heart has often been used as a temporary measure until a permanent human donor heart can be located, a number of recipients have not fared well, even for a limited duration. In addition, it is often unclear how long the recipient will have to wait for a donor. Proponents of the artificial heart hope that technological advances will allow the permanent replacement of human hearts with artificial ones.

See circulatory system; heart disease.

coronary heart disease: see coronary artery disease.

congestive heart failure, inability of the heart to expel sufficient blood to keep pace with the metabolic demands of the body. In the healthy individual the heart can tolerate large increases of workload for a considerable length of time. Cardiac failure results from conditions, e.g., coronary artery disease, hypertensive heart disease (see hypertension), valvular insufficiency, and rheumatic heart disease, that interfere with the nutrition and oxygenation of the heart muscle itself. Congestive heart failure develops in 50% to 60% of patients with such disorders, and it can be either acute or chronic. If the heart has time to compensate, the heart muscle may become hypertrophic (enlarged); this is caused by structural changes that impede blood flow and impair the ability of the heart to relax. Eventually the great demand for oxygen by the heart muscle cells cannot be met, and cell death results. Either the left or right ventricle alone may fail first, although combined failure is most common and almost always eventually occurs. Left ventricular failure is marked by shortness of breath (dyspnea), often accompanied by cough; pulmonary congestion and edema are evident. Failure of the right ventricle produces systemic edema, reflecting hepatic and visceral engorgement. Diagnosis is often confirmed by echocardiography. Treatment of cardiac failure usually includes dietary changes, restrictions on physical activity, rest, oxygenation, measures to improve myocardial contractility, and correction of arrhythmias. Restriction on sodium intake and the administration of diuretics (the dosages of which depend on the patient's weight) are used to remove excess sodium and water from the body. Digitalis is often prescribed to increase the speed and force of cardiac contractions, and ACE inhibitors are used to decrease peripheral vascular resistance, making heart pumping easier and more effective.

congenital heart disease, any defect in the heart present at birth. There is evidence that some congenital heart defects are inherited, but the cause of most cases is unknown. One known cause is infection of the mother with the rubella (German measles) virus during the first trimester of pregnancy. Among the most common congenital heart disorders are malformations in the valves and the persistence of structures that are normally closed off at birth, i.e., the ductus arteriosis (the fetal blood vessel that shunts blood from the pulmonary vein to the aorta, bypassing the heart) and the foramen ovale (the opening between the left and right atria of the fetal heart). If the malformation is severe, it will produce various symptoms of insufficient heart function, such as cyanosis (a bluish tinge to the skin), dyspnea (difficulty in breathing), fatigue, and abnormal heartbeat; valvular deformities predispose the patient to bacterial infection of the endocardium (see endocarditis). Less severe malformations may not produce noticeable symptoms until later in life, and some may not require any medical attention. Many congenital heart defects that are debilitating can be corrected surgically. Other congenital anomalies, such as Down syndrome, are present in about 20% of cases of congenital heart disease. See also heart disease.

bleeding heart: see fumitory.

athlete's heart, common term for an enlarged heart associated with repeated strenuous exercise. As a result of the increased workload required of it, the heart will increase physiologically by enlarging chambers and muscle mass, or hypertrophy by enlarging the size of the chambers and increasing the volume of blood pumped per stroke. Consequently, the heart has to contract less frequently and at rest will beat as few as 40 times per minute as compared with an average number of 70 beats in a normal heart. The condition is not pathological, and there is generally no danger of cardiac disability arising from it.

artificial heart: see heart, artificial.

Richard Lion-Heart: see Richard I, of England.

Heart, river, 180 mi (290 km) long, rising in the low prairie country near the Little Missouri River, SW N.Dak., and flowing E to the Missouri at Mandan, N.Dak. The Heart Butte and Dickinson dams, irrigation and flood control units built by the U.S. Bureau of Reclamation as part of the Missouri River basin project, have created the region's largest lakes, which are major recreation areas.

Any surgical procedure opening the heart and exposing one or more of its chambers, most often to repair valve disease or correct congenital heart malformations (see congenital heart disease). Invention of the heart-lung machine (see artificial heart), which allows the heart to be stopped during surgery, made it possible. The first successful open-heart surgery was performed in the U.S. in 1953 by John H. Gibbon, Jr., to close an atrial septal defect.

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or ischemic heart disease

Progressive reduction of blood supply to the heart muscle due to narrowing or blocking of a coronary artery (see atherosclerosis). Short-term oxygen deprivation can cause angina pectoris. Long-term, severe oxygen depletion causes a heart attack. Coronary bypass or angioplasty is needed if medication and diet do not control the disease.

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Procedure to remove a diseased heart and replace it with a healthy one from a legally dead donor. The first was performed in 1967 by Christiaan Barnard. The diseased heart is removed (except for some atrial tissue to preserve nerve connections to the natural pacemaker). The new heart is put in place and connected to the recipient's blood vessels. Patients and donors are matched for tissue type, but the patient's immune system must still be suppressed to prevent rejection (see immunosuppression). A successful transplant can enable the recipient to have an active life for many years.

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Inability of one or both sides of the heart to pump enough blood for the body. Causes include pulmonary heart disease, hypertension, and coronary atherosclerosis. A person with left-sided heart failure experiences shortness of breath after exertion, difficulty in breathing while lying down and night breathlessness, and abnormally high pressure in the pulmonary veins. A person with right-sided failure experiences abnormally high pressure in the systemic veins, liver enlargement, and accumulation of fluid in the legs. A person with failure of both ventricles has an enlarged heart and a three-beat heartbeat. Treatment includes bed rest, medications such as digitalis, control of excess salt and water retention, and elimination of the underlying cause. Seealso congestive heart failure.

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or myocardial infarction

Death of a section of heart muscle when its blood supply is cut off, usually by a blood clot in a coronary artery narrowed by atherosclerosis. Hypertension, diabetes mellitus, high cholesterol, cigarette smoking, and coronary heart disease increase the risk. Symptoms include severe chest pain, often radiating to the left arm, and shortness of breath. Up to 20percnt of victims die before reaching the hospital. Diagnosis is done by electrocardiography and by analysis for enzymes in the blood. Treatment aims to limit the area of tissue death (infarct) and prevent and treat complications. Thrombolytic (clot-dissolving) drugs may be administered. Beta-blockers alleviate pain and slow the heart rate. Angioplasty or coronary bypass restores blood flow to heart muscle. Follow-up may include drugs, exercise programs, and counseling on diet and lifestyle changes.

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Organ that pumps blood, circulating it to all parts of the body (see circulation). The human heart is a four-chambered double pump with its right and left sides fully separated by a septum and subdivided on both sides into an atrium above and a ventricle below. The right atrium receives venous blood from the superior and inferior venae cavae (see vena cava) and propels it into the pulmonary circulation. The left atrium takes in blood from the pulmonary veins and sends it into the systemic circulation. Electrical signals from a natural pacemaker cause the heart muscle to contract. Valves in the heart keep blood flowing in one direction. Their snapping shut after each contraction causes the sounds heard as the heartbeat. Seealso cardiovascular system.

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Deformity of the heart. Examples include septal defect (opening in the septum between the sides of the heart), atresia (absence) or stenosis (narrowing) of one or more valves, tetralogy of Fallot (with four components: ventricular septal defect, pulmonary valve stenosis, right ventricular enlargement, and positioning of the aorta so that it receives blood from both ventricles), and transposition of the great vessels (so the pulmonary and systemic circulations each receive blood from the wrong side of the heart). Such defects can prevent enough oxygen from reaching the tissues, so the skin has a bluish cast. Many are fatal if not corrected surgically soon after birth—or, rarely, before birth, if detected prenatally. Abnormalities of the large vessels are usually less serious (see aorta, coarctation of; ductus arteriosus).

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Any of several species of Dicentra, a genus of herbaceous flowering plants of the fumitory family (Fumariaceae). The old garden favourite is the Japanese D. spectabilis, which has small rosy-red and white, heart-shaped flowers dangling from arching stems. The eastern, or wild, bleeding heart (D. eximia) produces sprays of small pink flowers from April to September in the Allegheny Mountains region of the U.S. The Pacific, or western, bleeding heart (D. formosa), ranging from California to British Columbia, has several varieties of garden interest.

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Machine or mechanical pump that maintains blood circulation in the human body. The heart-lung machine, a mechanical pump, can maintain circulation for a few hours while the heart is stopped for surgery. It shunts blood away from the heart, oxygenates it, and returns it to the body. No device has yet been developed for total, long-term replacement of the heart; existing artificial hearts reduce the heart's workload by pumping between beats or acting as an auxiliary ventricle and are suitable only as temporary replacements in patients awaiting transplant. Seealso pacemaker.

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