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:
“And my heart is like nothing so much as a bowl
Brimming over with quivering curds!”
—Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)
“For like as herbs and trees bringen forth fruit and flourish in May, in likewise every lusty heart that is in any manner a lover, springeth and flourisheth in lusty deeds.”
—Thomas Malory (c. 1430–1471)
“Do not give heed to everything that people say, or you may hear your servant cursing you; your heart knows that many times you have yourself cursed others.”
—Bible: Hebrew, Ecclesiastes 7:21.