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:
“Lovers, the conclusion is
Doubled sighs and jealousies
In a single heart that grieves
For lost honour among thieves.”
—Robert Graves (1895–1985)
“It isn’t enough for your heart to break because everybody’s heart is broken now.”
—Allen Ginsberg (b. 1926)
“Hear my soul speak:
The very instant that I saw you, did
My heart fly to your service, there resides
To make me slave to it.”
—William Shakespeare (1564–1616)