The heart is a hollow muscle that pumps blood throughout the blood vessels by repeated, rhythmic contractions. It is found in all animals with a circulatory system (including all vertebrates).
The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδιά, kardia, for "heart".
The vertebrate heart is principally composed of cardiac muscle and connective tissue. Cardiac muscle is an involuntary striated muscle tissue found only in this organ and responsible for the ability of the heart to pump blood.
The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average 66 year lifespan. It weighs approximately 250 to 300 grams (9 to 11 oz) in females and 300 to 350 grams (11 to 12 oz) in males.
Read more about Heart: Structure, The Invertebrate Heart, Functioning, Early Development, History of Discoveries, Additional Images
Famous quotes containing the word heart:
“Hope deferred makes the heart sick, but a desire fulfilled is a tree of life.”
—Bible: Hebrew, Proverbs 13:12.
“I pity the men whose natural pleasures are burthens, and who fly from joy ... as if it was really an evil in itself.... Poor unfortunate creature that he is! as if the causes of anguish in the heart were not enow—but he must fill up the measure, with those of caprice; and not only walk in a vain shadow,—but disquiet himself in vain too.”
—Laurence Sterne (1713–1768)
“The hearts of small children are delicate organs. A cruel beginning in this world can twist them into curious shapes. The heart of a hurt child can shrink so that forever afterward it is hard and pitted as the seed of a peach. Or, again, the heart of such a child may fester and swell until it is misery to carry within the body, easily chafed and hurt by the most ordinary things.”
—Carson McCullers (1917–1967)