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:
“At the heart of the matter of masculine excess is a great longing for the love and approval of a father, a man who can tell another man that his masculinity is splendid enough and he can now relax.”
—Frank Pittman (20th century)
“I turn my head to sky rains falling,
wash the wounds of numbness from my soul.
Turn my heart in tides of fierce renewal,
where love and rage run whole.
Come drink deep.”
—Carolyn McDade (20th century)
“The Japanese do not fear God. They only fear bombs.”
—Jerome Cady, U.S. screenwriter. Lewis Milestone. Yin Chu Ling, The Purple Heart (1944)