A pulmonary embolism is a blood clot or piece of fat blocking an artery in the lung.
Clots can develop in any vein, break loose, and go to the lungs.
Causes Most pulmonary embolisms are clots that come from deep veins in the legs or pelvis. Fatty embolisms usually come from a break in a bone or, during pregnancy, from amniotic fluid. This type of embolism occurs less frequently. Chances of a blood clot forming increase if you sit or lie in one spot for a long time. Surgery, heart problems, and taking birth control pills also increase your chances of forming a clot.