The heart is present in all vertebrates. It plays the role of pumping blood to all parts of our body through the blood vessels. The human heart is composed of a muscle called cardiac muscle. 72 beats per minute is the rate that a human heart beats on an average. Our heart is more or less like a pump. The heart has 4 valves namely tricuspid valve, mitral valve, pulmonary valve and semilunar valve. The human heart is placed in between our 2 lungs. The size of the human heart is roughly about the size of the human fist.