When oxygenated blood comes into felt atriums, it contracts and pours blood into the left ventricle. From left ventricle the oxygenated blood is distributed to all parts of the body through aorta and arteries.
 The veins collect the deoxygenated blood from different parts of the body and pours it into vena- cava. vena-cava in turn pours it into the right artrium. From there the blood pours into right ventricle. Right ventricle pumps the blood to lungs for oxygenation through pulmonary artery. Oxygenated blood is brought back to left artrium through pulmonary vein to complete the circulation. this process is also called double- circulation.
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