Pulmonary embolism, as the name implies, is a series of pathophysiological changes caused by an embolus blocking the pulmonary artery. Most of the emboli we often refer to are blood clots, so this article focuses on pulmonary thromboembolism. Unlike in situ thrombus in coronary artery of coronary heart disease, pulmonary thrombus is basically from the source of body circulation, which is commonly found in the lower extremities and abdominal deep vein system. What are the symptoms of pulmonary embolism? It mainly depends on the area of embolism and the underlying cardiopulmonary function of the patient. The physiological effects of pulmonary embolism mainly include the effects on circulation and pulmonary oxygenation. If the area of pulmonary embolism is too large, the blood cannot return to the left ventricle as an engine, it will be silted to in the right ventricle, resulting in the extreme expansion of the right ventricle in the short term, thus compressing the wall of the left ventricle, the blood flow to the left ventricle will be even less, the patient’s blood pressure will be reduced, even shock and sudden death. The lower blood pressure will affect the blood flow in the coronary arteries, and together with the high pressure in the right ventricular wall compressing the coronary arteries, some patients will have angina-like symptoms of myocardial ischemia. In addition, the blood in the venous system is blocked by the embolus and cannot flow through the alveolar capillary network, which prevents air-blood exchange and leads to hypoxia, and the patient will have reflexive shortness of breath, which is more obvious after activity. If the bronchial artery of the lung is not able to compensate for the blockage of small thrombus, it will cause ischemic necrosis of the lung, i.e. pulmonary infarction, and the patient will have chest pain, fever and other symptoms similar to pneumonia. The treatment of pulmonary embolism is divided into thrombolysis and anticoagulation. For large life-threatening thrombosis, immediate thrombolysis is needed. For life-threatening massive thrombosis, immediate thrombolysis is required. In contrast, more than 90% of patients in clinical practice have non-massive pulmonary embolism, so anticoagulation therapy to prevent further thrombosis can be improved by the patient’s own thrombolytic mechanism. In conclusion, pulmonary embolism is not an uncommon disease. If you have asymmetric edema of the lower extremities, or if you are bedridden, travel long distances, have recent major surgery, have cancer, or are pregnant, you need to seek hospital consultation once you have symptoms such as dyspnea, hemoptysis, and chest pain.