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High Quality Content by WIKIPEDIA articles! The heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek kardia, for "heart." The vertebrate heart is composed of cardiac muscle, an involuntary striated muscle tissue which is found only within this organ. The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average lifespan. It weighs on average 250 g to 300 g in females and 300 g to 350 g in males.