Whether a pleural effusion is serious or not needs to be judged according to the cause, the amount and the speed of growth of the pleural effusion. There are many reasons for the occurrence of pleural effusion, such as infectious diseases (pneumonia, tuberculosis, etc.), malignant tumors, autoimmune diseases, and bleeding from chest trauma. If the patient’s pleural effusion is produced slowly and the amount of effusion is small, the symptoms are mild; if the pleural effusion increases faster and in larger amount in a short period of time, the symptoms are more severe. Because a large amount of pleural effusion will cause the chest cavity to be occupied by too much fluid and the lung tissue to be compressed, which in turn will produce symptoms such as chest tightness and dyspnea. A large amount of pleural effusion often suggests that the effusion is due to malignant tumors. Pleural effusion is usually caused by other diseases, so the main focus is on treating the primary disease, and the effusion can be drained by puncture or tube placement when the amount of effusion is large. Patients should not be too anxious, just relax and cooperate with the doctor for treatment. If chest tightness and shortness of breath have increased significantly recently, patients should go to hospital for treatment in time.