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:
“Only ambition is fired by the coincidences of success and easy accomplishment but nothing is quite as splendidly uplifting to the heart as the defeat of a human being who battles against the invincible superiority of fate. This is always the most grandiose of all tragedies, one sometimes created by a dramatist but created thousands of times by life.”
—Stefan Zweig (18811942)
“While I wrought out these fitful Danaan rhymes,
My heart would brim with dreams about the times
When we bent down above the fading coals
And talked of the dark folk who live in souls
Of passionate men, like bats in the dead trees....”
—William Butler Yeats (1865–1939)
“And wilt thou leave me thus?
That hath loved thee so long
In wealth and woe among:
And is thy heart so strong
As for to leave me thus?
Say nay! say nay!”
—Sir Thomas Wyatt (1503?–1542)