Deoxygenated blood enters at the vena cava. The right atrium receives the blood, and it then passes into the right ventricle. From there it goes to the lungs via the pulmonary artery. This brings the deoxygenated blood to the lungs, where gas exchange takes place.The blood then returns from the lungs to the heart via the pulmonary vein, which leads into the left atrium. The blood then moves through to the left ventricle, from where it is pumped around the body. It leaves the heart via the aorta