heart

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 .

heart the heart is traditionally regarded as the centre of a person's thoughts and emotions, especially love or compassion.

The heart is stylistically represented by two equal curves meeting at a point at the bottom and a cusp at the top; such hearts are emblematic of love.

Hearts are one of the four suits in a conventional pack of playing cards, denoted by a stylized red figure of a heart.
break someone's heart overwhelm someone with sadness.
have a heart of gold have a generous nature.
have one's heart in one's mouth be greatly alarmed or apprehensive.
heart of darkness a place of savagery and barbarism, from the title of Joseph Conrad's novel (1902).
Heart of Dixie an informal name for Alabama.
Heart of Midlothian a name for the old Edinburgh Tolbooth, or prison, taken by Scott as the title of a novel (1818), set in 18th-century Edinburgh and opening with the Porteous riot.
heart of oak the solid central part of an oak tree as the traditional timber for ships. The phrase was popularized by the 18th-century song, ‘Heart of oak are our ships, heart of oak are our men.’
heart of stone a stern or cruel nature.
heart's blood an archaic term for the blood, as being necessary for life; vital energy or force.
one's heart's desire a person or thing that one greatly wishes for.

See also cold hands, warm heart, faint heart never won fair lady, heartbeat, hearts, hope deferred makes the heart sick, please your eye and plague your heart, it is a poor heart that never rejoices, a song in one's heart, put a stout heart to a stey brae, the way to a man's heart, wear one's heart on one's sleeve.

heart Muscular organ that pumps blood through the body. In humans, the heart muscle is located behind the sternum. Divided longitudinally by a muscular wall, the right side contains only deoxygenated blood, the left side only oxygenated blood. The pulmonary artery carries deoxygenated blood from the heart to the lungs. Each side divides into two chambers, an atrium and a ventricle. The average heart beat rate for an adult at rest is 70–80 beats per minute.