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:
“A torn jacket is soon mended; but hard words bruise the heart of a child.”
—Henry Wadsworth Longfellow (20th century)
“The wind’s on the wold
And the night is a-cold,
And Thames runs chill
‘Twixt mead and hill.
But kind and dear
Is the old house here
And my heart is warm
Midst winter’s harm.”
—William Morris (1834–1896)
“I haven’t the heart to poke poor Billy.”
—Harry Graham (1874–1936)