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 heart of another is a dark forest, always, no matter how close it has been to one’s own.”
—Willa Cather (1873–1947)
“When the sheep are in the fauld, and the kye at hame,
And a’ the warld to rest are gane,
The waes o’ my heart fa’ in showers frae my e’e,
While my gudeman lies sound by me.
Young Jamie lo’ed me weel, and sought me for his bride;”
—Lady Anne Lindsay (1750–1825)
“Those to whom God has imparted religion by feeling of the heart are very fortunate and are rightly convinced. But to those who do not have it, we can give it only by reasoning, waiting for God to give it by feeling of the heart—without which faith is only human and useless for salvation.”
—Blaise Pascal (1623–1662)