The pulmonary vein brings in oxygenated blood from the lungs through the left atrium and ventricle up into the aorta which then carries the oxygenated blood through the body. The vena cava (main vein) on the right side carries deoxygenated blood through the right atrium through the right ventricle up into the pulmonary artery, which carries the deoxygenated blood to the lungs to get oxygenated again. The pulmonary artery is the only artery to carry deaoxygenated blood.