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:
“A heart that overflows may seek out merrymaking and boisterous festivities to quietly rejoice, unnoticed amidst the reveling crowds.”
—Franz Grillparzer (1791–1872)
“Home—that blessed word, which opens to the human heart the most perfect glimpse of Heaven, and helps to carry it thither, as on an angel’s wings.”
—Lydia M. Child (1802–1880)
“I am considered a misanthropist now and then, because I do not socialize with many people. But it’s only my mind that avoids you, my heart is still with you, and seeks the distance so that it can keep on loving you.”
—Franz Grillparzer (1791–1872)