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 καρδιά, kardia, for "heart."

The vertebrate heart is composed of cardiac muscle, which is an involuntary striated muscle tissue 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 66 year lifespan. It weighs on average 250 g to 300 g in females and 300 g to 350 g in males.