There are many diseases that can cause pericardial effusion, many of which are not specific to the heart itself. It is relatively rare for pericardial effusion to occur as a result of myocardial infarction, severe aortic coarct with blood infiltration, or heart rupture. More common are hypothyroidism, long-term hormone use, rheumatic diseases, viral infections, bacterial infections or protozoal infections, which may also cause pericardial effusion, and malignant tumors, which may also cause pericardial effusion. If a small amount of pericardial effusion is found in a normal adult during a physical examination, most of them do not require treatment and should only be observed regularly. If a medium to large amount of pericardial effusion is found on a heart ultrasound, the condition may be more serious and must be sought and treated according to the cause. A large amount of pericardial effusion may lead to severe dyspnea, reduced ejection fraction, and heart failure.