Pulmonary embolism is the occlusion of one or more pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the lower extremities. Risk factors are conditions that impair venous return, conditions that cause endothelial injury or dysfunction, and underlying hypercoagulable states. Symptoms are nonspecific and include dyspnea, pleuritic chest pain, cough, and, in severe cases, syncope or cardiorespiratory arrest. Signs are also nonspecific and may include tachypnea, tachycardia, and hypotension. Diagnosis is based on an angiogram, perfusion scan, or a pulmonary arteriogram. Treatment is with anticoagulants, thrombolytics, or surgical removal.