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:
“Be near me when my light is low,
When the blood creeps, and the nerves prick
And tingle; and the heart is sick,
And all the wheels of Being slow.”
—Alfred Tennyson (1809–1892)
“All is changed. All looks strange to me and gives me a feeling which I would rather get away from, although I know it to be the carrying out of natural laws. And I am not complaining. I am doing the same as many old people have done, I suppose, who have led an active life and suddenly find themselves living without a purpose. Oh, my heart is so full. I could write a big book on the subject of going out of this world gracefully.”
—Maria D. Brown (1827–1927)
“I said to Heart, “How goes it?” Heart replied: “Right as a Ribstone Pippin!” But it lied.”
—Hilaire Belloc (1870–1953)