Pleural effusion does not usually cause pain because the pleura does not come into contact with friction at this time so it does not cause pain. Pleural effusion is a pathologic accumulation of fluid inside the cavity that exists between the visceral and mural pleura. Normally, there is about 5-15 ml of fluid in the pleural cavity, which acts as a lubricant between the two sides of the pleura. When pleural effusion is small, the patient’s symptoms are not obvious. When pleural effusion exceeds 500 ml, the pressure in the pleural cavity increases a lot, so symptoms of chest tightness, shortness of breath, palpitations, and dyspnea may occur. Although pleural effusion does not usually cause chest pain, too much pleural effusion can still bring great harm to the body. Therefore, once pleural effusion occurs, you should go to the hospital to find out the cause of the disease and then actively eliminate it.