When it comes to pulmonary thromboembolism, most people probably do not necessarily know about it. However, when it comes to myocardial infarction, any reader with a little medical knowledge will know. Domestic and international medical statistics have found that the incidence of pulmonary thromboembolism has reached half the incidence of myocardial infarction, and both are important causes of sudden death. As people become more aware of the disease, the number of cases that have been missed or neglected in the past will increase accordingly, and the overall incidence will rise. Compared to myocardial infarction, pulmonary thromboembolism is even more dangerous and has higher rates of death and disability than the former. The clinical manifestations of pulmonary thromboembolism are usually nonspecific and therefore can be easily confused with other cardiovascular diseases, making diagnosis difficult. The severity of clinical symptoms is not only related to the size of thrombus and the extent of embolism, but also closely related to the combination of other cardiac and pulmonary diseases. (A) Severe disease: Sudden onset of extreme dyspnea with severe hypoxic manifestations, also accompanied by angina pectoris, syncope and shock, often leading to ventricular fibrillation and cardiac arrest due to right heart failure and rapid death. This is caused by extensive pulmonary artery thromboembolism. (b) Minor symptoms: Anterior chest pain or hemoptysis, and often syncope and elevated blood pressure due to the combination of other cardiac and pulmonary diseases. (c) Other symptoms: Patients may also have adult respiratory distress syndrome due to small intra-pulmonary artery thrombosis, or fever and jaundice due to pulmonary infarction. Causes and predisposing factors The majority (90%) of the thrombi blocking the pulmonary arteries originate from the deep veins of the lower extremities. The thrombus in the deep vein is dislodged for various reasons and returns to the right heart system, where it becomes lodged in the pulmonary artery and eventually causes the disease. The predisposing factors for DVT are as follows: (a) Blood stasis in the lower extremities. The so-called “economy class syndrome” is the most typical example of this condition. In the small space of economy class, the lower extremities are restricted and cannot be fully extended. (2) The blood is in a hypercoagulable state. Some diseases such as nephrotic syndrome, hematologic diseases and familial thrombotic diseases usually have their blood in a hypercoagulable state and are prone to thrombosis. (iii) The blood vessel itself is damaged. For example, damage to the intima of blood vessels occurs by trauma, as well as having vascular sclerosis or degenerative changes. Prevention (a) Reduce blood stasis in the lower extremities and promote venous reflux. For example, when traveling long distances, do not sit still in a fixed position for a long time, and move the lower limbs regularly. Patients who are bedridden for a long time should have frequent leg massage if they cannot get out of bed. (ii) Drink water appropriately every day to reduce blood viscosity. Treat the corresponding disease, or take anticoagulant drugs to eliminate blood hypercoagulation. (iii) Eat a balanced diet, reduce cholesterol intake appropriately, quit smoking, exercise and control body weight. Treatment (i) Tethering. This treatment is aimed at patients with early onset of the disease (within 2 weeks), and thrombolytic drugs are administered intravenously to dissolve the blood clot. The earlier the treatment is given, the better the outcome is usually. (ii) Placement of a venous filter. Interventional placement of a filter in the inferior vena cava can effectively prevent thrombus dislodged from the deep veins of the lower extremities from entering the heart and causing further pulmonary artery thromboembolism. (iii) Surgery. It is suitable for patients with acute massive pulmonary thromboembolism, urgent condition and contraindication to thrombolysis, or patients with chronic pulmonary tethering. With the above treatments, it is possible to save the lives of most patients. Therefore, the key to treatment is to have a full understanding of the disease and to focus on prevention, as well as to achieve early diagnosis and early treatment.