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:
“My heart leaps up when I behold
A rainbow in the sky:”
—William Wordsworth (1770–1850)
“To revolutionize, at one effort, the universal world of human thought, human opinion, and human sentiment.... All that he has to do is to write and publish a very little book. Its title should be simple—a few plain words—”My Heart Laid Bare.” But—this little book must be true to its title.”
—Edgar Allan Poe (1809–1849)
“But what comes out of the mouth proceeds from the heart, and this is what defiles. For out of the heart come evil intentions, murder, adultery, fornication, theft, false witness, slander.”
—Bible: New Testament, Matthew 15:18,19.