After birth, the fetus usually has a small amount of pericardial effusion, as we normally have a small amount of fluid in the pericardium, but because the heart is smaller in children, the amount of fluid may appear to be larger. However, the amount of fluid will slowly disappear as the child grows, unless the fetus has a combination of pericardial mesothelioma, pericardial cysts, or other infectious or neoplastic factors, otherwise the fluid may be absorbed quickly without major hemodynamic problems. However, if the amount of pericardial effusion is very large after birth, regardless of the cause, we should actively insert a tube for drainage, and after drainage, improve the systolic and diastolic function of the heart, in order to alleviate the prognosis, which is the basic principles of management of pericardial effusion after birth.