Deep vein thrombosis is a blood clot or thrombus in a deep vein. It is most common in the leg. But one may develop in the arm or other part of the body. Part of the clot, called an embolus, can break off and travel to the lungs. This is a pulmonary embolus (PE). This can cut off the flow of blood. PE is an emergency and may cause death. If you have symptoms that may mean a blood clot in the lungs, call 911 or get emergency help. Symptoms of a blood clot in the lungs include chest pain, trouble breathing, coughing (may cough up blood), a fast heartbeat, sweating, and fainting.