[Pulmonary embolism].

A pulmonary embolism occurs when a blood clot moves through the bloodstream and becomes lodged in a blood vessel in the lungs. This can make it hard for blood to pass through the lungs to get oxygen. Diagnosing a pulmonary embolism can be difficult because half of patients with a clot in the lungs have no symptoms. Others may experience shortness of breath, chest pain, dizziness, and possibly swelling in the legs. If you have a pulmonary embolism, you need medical treatment right away to prevent a blood clot from blocking blood flow to the lungs and heart.