Why is blood circulation in human heart called double circulation? [NCERT Exemplar]

Why is blood circulation in human heart called double circulation? [NCERT Exemplar] Answer - The blood circulation in human heart is called double circulation because the blood passes through the heart twice in one complete cycle of the body i.e., once through the right half in the form of deoxygenated blood and once through the left half in the form of oxygenated blood.