The human heart consists of two pumps side by side and joined together by a dividing wall called the septum.Both pumps work together. The right side pumps deoxygenated blood from the body to the lungs and the left side pumps oxygenated blood from the lungs to the body.The blood in the two sides of the heart do not mix.The heart is made of cardiac muscle which contracts and relaxes in a regular rhythm about 60 times a minute.Cardiac muscle is myogenic and does not need electrical stimulation from the nervous system to contract but contracts by itself.Cardiac muscle does not fatigue like skeletal muscle.The heart is surrounded by inelastic pericardial membranes which prevent it from over-distending with blood.