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:
“He has outsoared the shadow of our night;
Envy and calumny and hate and pain,
And that unrest which men miscall delight,
Can touch him not and torture not again;
From the contagion of the world’s slow stain
He is secure, and now can never mourn
A heart grown cold, a head grown grey in vain.”
—Percy Bysshe Shelley (1792–1822)
“Our destiny, our being’s heart and home,
Is with infinitude, and only there;
With hope it is, hope that can never die,”
—William Wordsworth (1770–1850)
“I concluded that I was skilled, however poorly, at only one thing: marriage. And so I set about the business of selling myself and two children to some unsuspecting man who might think me a desirable second-hand mate, a man of good means and disposition willing to support another man’s children in some semblance of the style to which they were accustomed. My heart was not in the chase, but I was tired and there was no alternative. I could not afford freedom.”
—Barbara Howar (b. 1934)