Double circulation of blood : In double blood circulation, first impure blood comes to the heart and then it is supplied to the lungs for purification. Then pure blood is collected and poured into heart and it is supplied to all the parts of the body. Double circulation comprises two types of circulation as :

1. Pulmonary circulation : It is the circulation in which impure blood from rt. ventricle of heart goes to lungs and after purification it is poured back into the heart (left auricle).

Significance : Due to it blood is purified.

Right auricle Fig. Double circulation of blood in mammals

2. Systemic circulation : It is the circulation in which pure blood from left ven heart is pumped to all the parts of the body and then impure blood is collected and poured into right auricle.