Pulmonary arteries. Coloured angiogram (X-ray or arteriogram) of the pulmonary arteries in a healthy lung. The common pulmonary artery in the chest divides into thick left and right branches which transport deoxygenated blood from the heart to the lungs. One of these thick branches (upper centre) is seen in a lung forming a network of smaller and smaller branches. In this way, blood is placed in contact with inhaled air, carbon dioxide leaves the blood and oxygen is taken up. The outline of the lung is visible. To obtain this pulmonary angiogram a radio-opaque dye was injected through a catheter into the bloodstream to enable the blood vessels to be seen on X-ray.