Heart

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:

    My heart burnt within me with indignation and grief; we could think of nothing else.... All night long we had only snatches of sleep, waking up perpetually to the sense of a great shock and grief. Every one is feeling the same. I never knew so universal a feeling.
    Elizabeth Gaskell (1810–1865)

    A man is relieved and gay when he has put his heart into his work and done his best; but what he has said or done otherwise shall give him no peace.
    Ralph Waldo Emerson (1803–1882)

    One hand stiff—heaviness of forties & menopause reduced
    by one heart stroke, lame now—wrinkles—a scar on
    her head, the lobotomy—ruin, the hand dipping downwards to
    death—
    Allen Ginsberg (b. 1926)