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:
“The Sound of battle fell upon my ear & heart all day yesterday—even after dark the cannon’s insatiate roar continued ...”
—Elizabeth Blair Lee (1818–?)
“Swift beating on his breast in sibylline frenzy blind
Because the heart in his blood-sodden breast had dragged him down into mankind ...”
—William Butler Yeats (1865–1939)
“Madame Pertelote, my worldes bliss,
Harkneth these blissful birdes how they sing,
And see the freshe flowers how they spring;
Full is mine heart of revel and solace!’
But suddenly him fell a sorrowful case,
For ever the latter end of joy is woe.”
—Geoffrey Chaucer (1340?–1400)