Angiograms (blood vessel X-rays) of a healthy lung from a 52 year old female (left) and the lung of 48 year old female patient affected by a blood clot, or embolism (right). The embolism has stopped the blood flow to the lower lobes of the lung. Pulmonary embolisms can be fatal, as the blood is quickly starved of oxygen. This embolism occurred after the patient was operated on for a cerebral aneurysm (dilated blood vessel).