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:
“What of the heart without her? Nay, poor heart,
Of thee what word remains ere speech be still?
A wayfarer by barren ways and chill,
Steep ways and weary, without her thou art,
Where the long cloud, the long wood’s counterpart,
Sheds doubled darkness up the labouring hill.”
—Dante Gabriel Rossetti (1828–1882)
“Continued traveling is far from productive. It begins with wearing away the soles of the shoes, and making the feet sore, and ere long it will wear a man clean up, after making his heart sore into the bargain. I have observed that the afterlife of those who have traveled much is very pathetic.”
—Henry David Thoreau (1817–1862)
“There comes Poe, with his raven, like Barnaby Rudge,
Three-fifths of him genius, and two-fifths sheer fudge.
Who talks like a book of iambs and pentameters,
In a way to make people of common sense damn metres,
Who has written some things quite the best of their kind,
But the heart somehow seems all squeezed out by the mind.”
—James Russell Lowell (1819–1891)