Pulmonary effusion is the accumulation of fluid in the pleural cavity. When the fluid accumulation is small, there may be no obvious symptoms, while when the fluid accumulation is large, symptoms such as palpitation and dyspnea may appear. 1. Pulmonary effusion has different manifestations depending on the amount of fluid. When the amount of fluid is small, there may be no obvious symptoms. When there is a large amount of fluid, symptoms such as shortness of breath, dyspnea and palpitations may occur. 2. According to the cause of the disease, there are also other symptoms. The main causes are tuberculous pleurisy, malignant tumor, infectious disease, cardiac insufficiency, liver abscess. (1) Tuberculous pleurisy may be accompanied by low-grade fever, cough, night sweats and other manifestations of tuberculosis. (2) Malignant tumors are accompanied by wasting and symptoms of the primary tumor. (3) Infectious diseases may have fever, cough and sputum. (4) Cardiac insufficiency may be accompanied by pulmonary edema and symmetrical edema of lower limbs. (5) Liver abscess may be accompanied by fever and pain in the right liver region. With the above symptoms, suspected pulmonary effusion must seek medical attention and timely treatment.