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:
“In the game of “Whist for two,” usually called “Correspondence,” the lady plays what card she likes: the gentleman simply follows suit. If she leads with “Queen of Diamonds,” however, he may, if he likes, offer the “Ace of Hearts”: and, if she plays “Queen of Hearts,” and he happens to have no Heart left, he usually plays “Knave of Clubs.””
—Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)
“I fairly confess that, acting as nature and simplicity dictated, no sooner did I see the once loved bosom of my Ferdinand free from those deformed demons which had crept in and filled up the vacant space, than beholding my natural home once more the seat of innocence and truth, my heart joyfully danced into its delightful abode.”
—Sarah Fielding (1710–1768)
“Night City was like a deranged experiment in Social Darwinism, designed by a bored researcher who kept one thumb permanently on the fast-forward button. Stop hustling and you sank without a trace, but move a little too swiftly and you’d break the fragile surface tension of the black market; either way, you were gone ... though heart or lungs or kidneys might survive in the service of some stranger with New Yen for the clinic tanks.”
—William Gibson (b. 1948)