double circulation

In mammals, the characteristic blood circulatory system. The heart is divided into two halves, each half working as a separate pump. One side of the heart pumps blood to the lungs and back to the heart. The other side of the heart pumps blood to all other parts of the body and back to the heart.

Deoxygenated blood – that is, blood with a reduced content of oxygen – is pumped to the lungs. Blood returning from the lungs is oxygenated – it is carrying as much oxygen as it is capable of carrying. Oxygenated blood is then pumped by the other half of the heart to all other parts of the body where oxygen is used in respiration in the body tissues. The deoxygenated blood is returned to the heart.