Pulmonary embolism is usually caused by venous embolism in the lower extremities. The common clinical symptoms are sudden onset of chest pain, coughing up blood and difficulty in breathing, and even impairment of consciousness and cardiac arrest. If a patient is considered to have a pulmonary embolism, he or she needs to complete relevant tests, including D-dimer, blood gas analysis, and cardiac ultrasound. Patients with pulmonary embolism usually have significantly elevated D-dimer, blood gas analysis may indicate hypoxemia or type I respiratory failure, and cardiac ultrasound may show changes in the right atrium and right ventricle. Tests to confirm pulmonary embolism include pulmonary artery CTA, magnetic resonance pulmonary angiography, pulmonary nuclear scintigraphy and pulmonary angiography.