Pulmonary embolism is a blockage in a pulmonary artery from a thrombus (blood clot) that has moved from a deep vein thrombosis (a blood clot that most often develops in the deep veins of the leg). What generally happens is this: Large fragments of thrombi break off and are carried with the bloodstream until they are lodged in the pulmonary arteries. This blocks the flow of blood through the heart, which may lead to death. After ischemic heart disease and stroke, pulmonary embolism is the third leading cause of death from heart disease and may be the most common preventable cause of death in hospitals. It is unsuspected in at least two-thirds of people who die from it.
Pulmonary embolism is more likely to occur in people with symptoms and signs of deep vein thrombosis. Risk for pulmonary embolism increases according to the number of risk factors the person has for deep venous thrombosis.