/hahrt/, n.
1. Anat. a hollow, pumplike organ of blood circulation, composed mainly of rhythmically contractile smooth muscle, located in the chest between the lungs and slightly to the left and consisting of four chambers: a right atrium that receives blood returning from the body via the superior and inferior vena cavae, a right ventricle that pumps the blood through the pulmonary artery to the lungs for oxygenation, a left atrium that receives the oxygenated blood via the pulmonary veins and passes it through the mitral valve, and a left ventricle that pumps the oxygenated blood, via the aorta, throughout the body.
2. Zool.
a. the homologous structure in other vertebrates, consisting of four chambers in mammals and birds and three chambers in reptiles and amphibians.
b. the analogous contractile structure in invertebrate animals, as the tubular heart of the spider and earthworm.
3. the center of the total personality, esp. with reference to intuition, feeling, or emotion: In your heart you know I'm an honest man.
4. the center of emotion, esp. as contrasted to the head as the center of the intellect: His head told him not to fall in love, but his heart had the final say.
5. capacity for sympathy; feeling; affection: His heart moved him to help the needy.
6. spirit, courage, or enthusiasm: His heart sank when he walked into the room and saw their gloomy faces.
7. the innermost or central part of anything: Notre Dame stands in the very heart of Paris.
8. the vital or essential part; core: the heart of the matter.
9. the breast or bosom: to clasp a person to one's heart.
10. a person (used esp. in expressions of praise or affection): dear heart.
11. a conventional shape with rounded sides meeting in a point at the bottom and curving inward to a cusp at the top.
12. a red figure or pip of this shape on a playing card.
13. a card of the suit bearing such figures.
14. hearts,
a. (used with a sing. or pl. v.) the suit so marked: Hearts is trump. Hearts are trump.
b. (used with a sing. v.) a game in which the players try to avoid taking tricks containing this suit.
15. Bot. the core of a tree; the solid central part without sap or albumen.
16. good condition for production, growth, etc., as of land or crops.
17. Also called core. Ropemaking. a strand running through the center of a rope, the other strands being laid around it.
18. after one's own heart, in keeping with one's taste or preference: There's a man after my own heart!
19. at heart, in reality; fundamentally; basically: At heart she is a romantic.
20. break someone's heart, to cause someone great disappointment or sorrow, as to disappoint in love: The news that their son had been arrested broke their hearts.
21. by heart, by memory; word-for-word: They knew the song by heart.
22. cross one's heart, to maintain the truth of one's statement; affirm one's integrity: That's exactly what they told me, I cross my heart!
23. do someone's heart good, to give happiness or pleasure to; delight: It does my heart good to see you again.
24. eat one's heart out, to have sorrow or longing dominate one's emotions; grieve inconsolably: The children are eating their hearts out over their lost dog.
25. from the bottom of one's heart, with complete sincerity. Also, from one's heart, from the heart.
26. have a heart, to be compassionate or merciful: Please have a heart and give her another chance.
27. have at heart, to have as an object, aim, or desire: to have another's best interests at heart.
28. have one's heart in one's mouth, to be very anxious or fearful: He wanted to do the courageous thing, but his heart was in his mouth.
29. have one's heart in the right place, to be fundamentally kind, generous, or well-intentioned: The old gentleman may have a stern manner, but his heart is in the right place.
30. heart and soul, enthusiastically; fervently; completely: They entered heart and soul into the spirit of the holiday.
31. in one's heart of hearts, in one's private thoughts or feelings; deep within one: He knew, in his heart of hearts, that the news would be bad.
32. lose one's heart to, to fall in love with: He lost his heart to the prima ballerina.
33. near one's heart, of great interest or concern to one: It is a cause that is very near his heart. Also, close to one's heart.
34. not have the heart, to lack the necessary courage or callousness to do something: No one had the heart to tell him he was through as an actor.
35. set one's heart against, to be unalterably opposed to: She had set her heart against selling the statue. Also, have one's heart set against.
36. set one's heart at rest, to dismiss one's anxieties: She couldn't set her heart at rest until she knew he had returned safely.
37. set one's heart on, to wish for intensely; determine on: She has set her heart on going to Europe after graduation. Also, have one's heart set on.
38. take heart, to regain one's courage; become heartened: Her son's death was a great blow, but she eventually took heart, convinced that God had willed it.
39. take or lay to heart,
a. to think seriously about; concern oneself with: He took to heart his father's advice.
b. to be deeply affected by; grieve over: She was prone to take criticism too much to heart.
40. to one's heart's content, until one is satisfied; as much or as long as one wishes: The children played in the snow to their heart's content.
41. wear one's heart on one's sleeve,
a. to make one's intimate feelings or personal affairs known to all: She was not the kind who would wear her heart on her sleeve.
b. to be liable to fall in love; fall in love easily: How lovely to be young and wear our hearts on our sleeves!
42. with all one's heart,
a. with earnestness or zeal.
b. with willingness; cordially: She welcomed the visitors with all her heart.
43. Archaic.
a. to fix in the heart.
b. to encourage.
[bef. 900; ME herte, OE heorte; c. D hart, G Herz, ON hjarta, Goth hairto; akin to L cor (see CORDIAL, COURAGE), Gk kardía (see CARDIO-)]

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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. See also cardiovascular system.
(as used in expressions)
heart clam
ischemic heart disease
open heart surgery

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  organ that serves as a pump to circulate (circulation) the blood. It may be a straight tube, as in spiders and annelid worms, or a somewhat more elaborate structure with one or more receiving chambers (atria) and a main pumping chamber (ventricle), as in mollusks. In fishes (fish) the heart is a folded tube, with three or four enlarged areas that correspond to the chambers in the mammalian heart. In animals with lungs—amphibians, reptiles, birds, and mammals—the heart shows various stages of evolution from a single to a double pump that circulates blood (1) to the lungs and (2) to the body as a whole.

 In humans and other mammals (mammal) and in birds (bird), the heart is a four-chambered double pump that is the centre of the circulatory system. In humans it is situated between the two lungs and slightly to the left of centre, behind the breastbone; it rests on the diaphragm, the muscular partition between the chest and abdominal cavity.

      The heart consists of several layers of a tough muscular wall, the myocardium. A thin layer of tissue, the pericardium, covers the outside, and another layer, the endocardium, lines the inside. The heart cavity is divided down the middle into a right and a left heart, which in turn are subdivided into two chambers. The upper chamber is called an atrium (or auricle), and the lower chamber is called a ventricle. The two atria act as receiving chambers for blood entering the heart; the more muscular ventricles pump the blood out of the heart.

 The heart, although a single organ, can be considered as two pumps that propel blood through two different circuits. The right atrium receives venous blood from the head, chest, and arms via the large vein called the superior vena cava and receives blood from the abdomen, pelvic region, and legs via the inferior vena cava. Blood then passes through the tricuspid valve to the right ventricle, which propels it through the pulmonary artery to the lungs (lung). In the lungs venous blood comes in contact with inhaled air, picks up oxygen, and loses carbon dioxide. Oxygenated blood is returned to the left atrium through the pulmonary veins. Valves in the heart allow blood to flow in one direction only and help maintain the pressure required to pump the blood.

      The low-pressure circuit from the heart (right atrium and right ventricle), through the lungs, and back to the heart (left atrium) constitutes the pulmonary circulation. Passage of blood through the left atrium, bicuspid valve, left ventricle, aorta, tissues of the body, and back to the right atrium constitutes the systemic circulation. blood pressure is greatest in the left ventricle and in the aorta and its arterial branches. Pressure is reduced in the capillaries (vessels of minute diameter) and is reduced further in the veins returning blood to the right atrium.

 The pumping of the heart, or the heartbeat, is caused by alternating contractions and relaxations of the myocardium. These contractions are stimulated by electrical impulses from a natural pacemaker, the sinoatrial, or S-A, node located in the muscle of the right atrium. An impulse from the S-A node causes the two atria to contract, forcing blood into the ventricles. Contraction of the ventricles is controlled by impulses from the atrioventricular, or A-V, node located at the junction of the two atria. Following contraction, the ventricles relax, and pressure within them falls. Blood again flows into the atria, and an impulse from the S-A starts the cycle over again. This process is called the cardiac cycle. The period of relaxation is called diastole. The period of contraction is called systole. Diastole is the longer of the two phases so that the heart can rest between contractions. In general, the rate of heartbeat varies inversely with the size of the animal. In elephants (elephant) it averages 25 beats per minute, in canaries (canary) about 1,000. In humans (human body) the rate diminishes progressively from birth (when it averages 130) to adolescence but increases slightly in old age; the average adult rate is 70 beats at rest. The rate increases temporarily during exercise, emotional excitement, and fever and decreases during sleep. Rhythmic pulsation felt on the chest, coinciding with heartbeat, is called the apex beat. It is caused by pressure exerted on the chest wall at the outset of systole by the rounded and hardened ventricular wall.

      The rhythmic noises accompanying heartbeat are called heart sounds. Normally, two distinct sounds are heard through the stethoscope: a low, slightly prolonged “lub” (first sound) occurring at the beginning of ventricular contraction, or systole, and produced by closure of the mitral and tricuspid valves, and a sharper, higher-pitched “dup” (second sound), caused by closure of aortic and pulmonary valves at the end of systole. Occasionally audible in normal hearts is a third soft, low-pitched sound coinciding with early diastole and thought to be produced by vibrations of the ventricular wall. A fourth sound, also occurring during diastole, is revealed by graphic methods but is usually inaudible in normal subjects; it is believed to be the result of atrial contraction and the impact of blood, expelled from the atria, against the ventricular wall.

      Heart “murmurs” may be readily heard by a physician as soft swishing or hissing sounds that follow the normal sounds of heart action. Murmurs may indicate that blood is leaking through an imperfectly closed valve and may signal the presence of a serious heart problem.

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Universalium. 2010.