heart is a muscular (muscle) organ (organ (anatomy)) 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 (Greek language) ??????, kardia, for "heart."

The vertebrate heart is composed of cardiac muscle, an involuntary striated muscle tissue which is found only within this organ (organ (anatomy)). 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 on average 250 g to 300 g in females and 300 g to 350 g in males.