Pulmonary embolism is a clinical and pathophysiological syndrome caused by endogenous or exogenous emboli blocking the main trunk or branches of the pulmonary artery, resulting in impaired pulmonary circulation. It includes pulmonary thromboembolism, fat embolism syndrome, amniotic fluid embolism, air embolism, tumor embolism, etc. The symptoms of pulmonary embolism are diverse, but they lack specificity. The severity of symptoms also varies greatly, and can range from asymptomatic and insidious to hemodynamic instability, or even fragmentation death. Common symptoms include: 1. chest pain: including pleuritic chest pain or angina-like pain. 2. 2, syncope: may be the only or the first symptom of pulmonary embolism. 3, hemoptysis: often a small amount of hemoptysis, large hemoptysis is rare. 4.Irritability: panic and even near-death feeling. 5.Unexplained dyspnea and shortness of breath: especially obvious after activity, which is the most common symptom of pulmonary embolism. 6.Cough, palpitation, etc.: Different combinations of the above symptoms may occur in each case. The so-called “triad of symptoms”, i.e. dyspnea, chest pain and hemoptysis at the same time, is sometimes seen clinically, but only in about 20% of patients. Therefore, the so-called triad of pulmonary embolism is actually rare. Signs: 1. Circulatory system signs: tachycardia; blood pressure change, in severe cases, blood pressure may drop or even shock; jugular vein filling or abnormal pulsation; second heart sound (P2) in the pulmonary valve area is hyperactive or split, systolic murmur in the tricuspid valve area. 2. Respiratory signs: shortness of breath is most common; cyanosis; rales and/or fine rales can sometimes be heard in the lungs, and vascular murmurs can occasionally be heard in the lung fields; the corresponding signs appear when pulmonary atelectasis and pleural effusion are combined. 3.Other: Fever, mostly low fever, can be accompanied by fever of 38℃ or more in a few patients.