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 last time I saw Paris
Her heart was warm and gay.”
—Oscar Hammerstein II (1895–1960)
“Blows the wind to-day, and the sun and the rain are flying,
Blows the wind on the moors to-day and now,
Where about the graves of the martyrs the whaups are crying,
My heart remembers how!”
—Robert Louis Stevenson (1850–1894)
“[He] didn’t dare to, because his father had a weak heart and habitually threatened to drop dead if anybody hurt his feelings. You may have noticed that people with weak hearts are the tyrants of English married life.”
—George Bernard Shaw (1856–1950)