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:
“When we have broken our god of tradition, and ceased from our god of rhetoric, then may God fire the heart with his presence.”
—Ralph Waldo Emerson (1803–1882)
“An Irishman’s heart is nothing but his imagination.”
—George Bernard Shaw (1856–1950)
“It is not worth the while to let our imperfections disturb us always. The conscience really does not, and ought not to monopolize the whole of our lives, any more than the heart or the head. It is as liable to disease as any other part.”
—Henry David Thoreau (1817–1862)