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:
“Not yet has my heart or head
In the least way realized
They and I are civilized.”
—Countee Cullen (1903–1946)
“Old women even forget how to love their sons. The heart gets worn out, Monsieur.”
—Albert Camus (1913–1960)
“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)