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:
“Who knows whither the clouds have fled?
In the unscarred heaven they leave no wake,
And the eyes forget the tears they have shed,
The heart forgets its sorrow and ache;
The soul partakes the season’s youth,
And the sulphurous rifts of passion and woe
Lie deep ‘neath a silence pure and smooth,
Like burnt-out craters healed with snow.”
—James Russell Lowell (1819–1891)
“‘Way down upon de Swanee ribber,
Far, far away,
Dere’s where my heart is turning ebber,
Dere’s where de old folks stay.”
—Stephen Collins Foster (1826–1884)
“If we had a keen vision and feeling of all ordinary human life, it would be like hearing the grass grow and the squirrel’s heart beat, and we should die of that roar which lies on the other side of silence. As it is, the best of us walk about well wadded with stupidity.”
—George Eliot [Mary Ann (or Marian)