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 world stands out on either side
No wider than the heart is wide;
Above the world is stretched the sky,—
No higher than the soul is high.”
—Edna St. Vincent Millay (1892–1950)
“My heart got to thumping. You can’t reason with your heart; it has its own laws, and thumps about things which the intellect scorns.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)
“The heart may think it knows better: the senses know that absence blots people out. We really have no absent friends. The friend becomes a traitor by breaking, however unwillingly or sadly, out of our own zone: a hard judgment is passed on him, for all the pleas of the heart.”
—Elizabeth Bowen (1899–1973)