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:
“The heart never grows better by age; I fear rather worse; always harder. A young liar will be an old one, and a young knave will only be a greater knave as he grows older.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“Intellectual life is international. Only a period of discouragement, an age that has given up on itself, that wants to “preserve,” that has been driven onto the defensive, can be intellectually nationalist. Such a period is essentially “conservative.” A person who has progress in his heart is international.”
—Robert Musil (1880–1942)