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 is the essence that inquires.
He is the axis of the star;
He is the sparkle of the spar;
He is the heart of every creature;
He is the meaning of each feature;
And his mind is the sky,
Than all it holds more deep, more high.”
—Ralph Waldo Emerson (1803–1882)
“At school boys become gluttons and slovens, and, instead of cultivating domestic affections, very early rush into the libertinism which destroys the constitution before it is formed; hardening the heart as it weakens the understanding.”
—Mary Wollstonecraft (1759–1797)
“He hath a heart as sound as a bell and his tongue is the clapper, for what his heart thinks, his tongue speaks.”
—William Shakespeare (1564–1616)