Double Circulation: In the human heart, blood passes through the heart twice in one cardiac cycle.This type of circulation is called double circulationDouble circulation ensures complete segregation of oxygenated and deoxygenated blood which is necessary for optimum energy production in warm-blooded animals.Circulation of Blood through the heart:Systemic Vein → Sinus Venosus → Right Auricle → Right Ventricle → Pulmonary Artery → Lungs → Pulmonary Vein → Left Auricle → Left Ventricle → Trunchus Arteriosus → Systemic Circulation\xa0
The blood that enter the human heart twice a time in a cardiac cycle is called double circulation

A ciculation in which a blood passes twice from a heart to complete one cycle is called double circulation.
The right side of the heart receives and pumps deoxygenated blood and left side of the heart receives and pumps oxygenated blood. This circulation is called double circulation.*The blood is pumped by the right ventricle and it enters the pulmonary artery whereas the left ventricle pumps blood into the aorta.The deoxygenated blood pumped into the pulmonary artery is passed onto the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium.This is called pulmonary pathway*The oxygenated blood entering the aorta is carried by the network of arteries, arterioles and capillaries to the tissues from where the deoxygenated blood is collected by a system of venules, veins and vena cava and passed into the right atrium. This is the systemic circulation.
When Blood passes twice in one cardiac cyclethen it is called double circulation of blood