These blood vessels contract and squeeze in time to the heart beat to
deliver oxygen-rich blood.

Your heart is really a muscle. Its located a little to the left of the middle of your chest, and it's about the size of your fist. There are lots of muscles all over your body in your arms, in your legs, in your back, even in your behind.  But the heart muscle is special because of what it does. The heart sends blood around your body. The blood provides your body with the oxygen and nutrients it needs. It also carries away waste.  Your heart is sort of like a pump, or two pumps in one. The right side of your heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite: It receives blood from the lungs and pumps it out to the body.

Explanation: