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:
“But the heart refuses to be imprisoned; in its first and narrowest pulses it already tends outward with a vast force and to immense and innumerable expansions.”
—Ralph Waldo Emerson (1803–1882)
“The impulse to perfection cannot exist where the definition of perfection is the arbitrary decision of authority. That which is born in loneliness and from the heart cannot be defended against the judgment of a committee of sycophants. The volatile essences which make literature cannot survive the clichés of a long series of story conferences.”
—Raymond Chandler (1888–1959)
“I pity the men whose natural pleasures are burthens, and who fly from joy ... as if it was really an evil in itself.... Poor unfortunate creature that he is! as if the causes of anguish in the heart were not enow—but he must fill up the measure, with those of caprice; and not only walk in a vain shadow,—but disquiet himself in vain too.”
—Laurence Sterne (1713–1768)