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 bone-frame was made for
no such shock knit within terror,
yet the skeleton stood up to it:
the flesh? it was melted away,
the heart burnt out, dead ember,
tendons, muscles shattered, outer husk dismembered....”
—Hilda Doolittle (1886–1961)
“One enemy, of many, who knows well
Your heart is luminous
In the watched dark, quivering through locks and caves,
Will pull the thunderbolts
To shut the sun, plunge, mount your darkened keys....”
—Dylan Thomas (1914–1953)
“The last time I saw Paris
Her heart was warm and gay.”
—Oscar Hammerstein II (1895–1960)