Pulmonary embolism occurs when a blood clot lodges in the blood vessels (pulmonary arteries) of the lung. This blood clot is called an embolus, and most often begins as a clot in the veins of the legs or pelvis. These clots may happen after surgery, particularly after surgery of the hip or pelvic area, or after an extended period of immobility such as a long auto or airplane trip. Some people have a tendency to form blood clots due to an abnormality in their blood clotting system.

Common signs and symptoms of pulmonary embolism include: sudden shortness of breath, chest pain, a cough that produces bloody sputum, sweating, a rapid heartbeat, and lightheadedness or fainting. These can vary greatly, depending on how much of the lung is involved, the size of the clot and a person’s overall health — especially the presence or absence of other lung or heart disease.