The heart is a double Cylinder pump with rhythmic propulsive power and intake and exhaust of essential requirements and distribution to the entire body uniformly and excretion of undesired execreants regularly without rest. The Heart receives the Blood from all parts of the body adds nutrients and oxygen after the ex-creates are removed from it to distribute to each and every organ of the entire body continuously to add what it needs endlessly from 1st to the last breath of man without requiring a watch of the brain. This is done while the Upper Chambers receive and Lower Chambers send and the Right chambers take blood from the entire body to send it to lungs to purify and the Left Chambers take the Oxygenated Blood from the lungs to send it to the entire body as needed.
SO that the oxygenated and deoxygenated blood can be divided into two chambers and we can get high efficiency.
a four - chambered heart avoids the mixing of oxygenated and deoxygenated blood. Thus it helps in meeting our energy needs.
So as to facilitate double-circulation in human body.
mammals(human beings) have igh energy requirements as they need energy to maintain their body temperature.Hence a 4 chambered heart would allow high efficient supply of oxygen necessary for enrgy requirements of mammals and birds.