Question

Why is pumping of blood by heart referred to as double circulation?

Answer 1

double circulation system deliver greater blood Flow rate to tissue around the body because the heart pumps (oxygenated or oxygen rich) blood returned to it from lungs. This is useful because when blood pass through the lungs it's pressure is reduse.

Answer 2

Human circulation is called double circulation because it perform two circualtion simantaseously
1)Pulmandory circulation
2)Systemic circulation