Two-thirds of the heart's mass is on the left side, between the lungs. The average heart weighs 11 ounces beats about 72 to 80 times per minute pumps about l,000 gallons of blood through the body each day is encased in a membrane, the pericardium . The interior of the heart contains four chambers and four valves.
Valves allow the blood to flow in only one direction, up or down.
The blood flows in with each contraction and relaxation of the heart, then travels from the auricles to the ventricles, then out to be distributed to the entire body. This system controls the circulation of blood through the body, via the heart and blood vessels, thereby supplying the cells of the body with the nutrients and oxygen it needs and removes waste products. There are two divisions of the vascular system. Lymph is derived from the blood and gradually deposited back into the blood stream. These two systems are intimately linked together.