The foramen ovale usually closes completely within the first year of life, but there are some acquired diseases that lead to excessive right atrial pressure, the foramen ovale can reopen and right-to-left shunting occurs. The difference between it and simple atrial septum is: simple atrial septum is congenital, usually left to right shunt, atrial septum combined with other malformations appearing right heart high pressure can also appear right to left shunt, usually the gap is larger; reopening is acquired, is right to left shunt, the gap is often smaller, often with other acquired diseases in the first.