The four chambered heart consists of 2 separate pumps that work simultaneously. The right side of the heart contains deoxygenated blood received from the body and is sent to lungs via pulmonary circulation. The left side of the heart works as another pump. It contains only oxygenated blood received from lungs and is sent to body through systemic circulation. Thus no mixing of oxygenated and deoxygenated blood occurs in the heart. The blood passes through the heart twice- pulmonary and systemic circulation. This type of circulation is known as double circulation.

Double circulation is necessary in human beings in order to avoid mixing of oxygenated and deoxygenated blood which makes the circulatory system more efficient and helps in maintaining a constant body temperature.