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It goes from the right ventricle to the left atrium.From the right ventricle it originates the pulmonary artery or trunk, which divides into right and left pulmonary arteries directed towards the hilum of the respective lungs.These are capillarized right inside the lungs, where carbon dioxide is released (CO 2 ) and oxygen is taken (O 2 ). The blood so charged with oxygen returns to the heart thanks to the four pulmonary veins, in correspondence of the left atrium.