Pulmonary Embolism What is it? A blood clot in the lung. It occurs when a clot, usually in the leg or pelvis, breaks free and gets stuck in a lung artery (pulmonary artery). The clot interrupts blood flow, making it more difficult for your lungs to provide oxygen to the rest of your body. Symptoms: Sudden, sharp chest pain often with shortness of breath Sudden, unexplained shortness of breath, even without pain Cough that may produce blood-streaked spit Rapid heartbeat with shortness of breath Fainting Severe anxiety Unexplained sweating Swelling of one leg only, caused by a blood clot in the leg Pulmonary embolism can be life-threatening. If you have symptoms of a pulmonary embolism, seek emergency medical help immediately.