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:
“Le coeur a ses raisons que la raison ne connait point. The heart has its reasons which reason does not know of.”
—Blaise Pascal (1623–1662)
“A man is relieved and gay when he has put his heart into his work and done his best; but what he has said or done otherwise shall give him no peace.”
—Ralph Waldo Emerson (1803–1882)
“Then one will say, ‘He is not dead, maybe,
Who was mortality’s unshaken lover
Who loved the spring upon the Tennessee,
The hushed fall and, again, the coming clover.’
None will recall, not knowing, the twisted roads
Where the mind wanders till the heart corrodes.”
—Allen Tate (1899–1979)