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:
“There are strings in the human heart that had better not be vibrated.”
—Charles Dickens (1812–1870)
“I know I have the body of a weak and feeble woman, but I have the heart and stomach of a king, and of a king of England, too.”
—Elizabeth I (1533–1603)
“While I wrought out these fitful Danaan rhymes,
My heart would brim with dreams about the times
When we bent down above the fading coals
And talked of the dark folk who live in souls
Of passionate men, like bats in the dead trees....”
—William Butler Yeats (1865–1939)