commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart There is contraction and relaxation of the muscles in the chambers of the heart which is responsible for the pumping of the blood to the parts of the body. The blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta.The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system The pumped blood carries oxygen  and nutrients  to the body, while carrying metabolic waste  such as carbon dioxide  to the lungs This pathway constitutes the pulmonary circulation. The oxygenated blood entering the aorta is carried by a network of arteries, arterioles and capillaries to the tissues from where the de-oxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is the systemic circulation. The type of blood circulation in humans is called as double circulation. These two processes pulmonary and systemic circulation are together called as double circulation. This process is necessary because the blood enters twice in the heart in a single cycle.

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