Atrial septal defects (AV defects) are very common in precordial disease. In particular, echocardiography can reveal a number of “atrial defects” in young infants under 1 year of age. Before birth, the foramen ovale in the middle of the fetal atrial septum is open. After birth, it closes gradually, some earlier, some later, but most of them close before the age of 1 to 1.5 years. Some hospitals report the unclosed foramen ovale as atrial defect, which does not require treatment up to 2 years of age. Of course, there are many others who do have atrial defect and if it is large, it is mandatory to treat it. Since atrial defect develops slowly in pediatric age and some small atrial defects have the possibility of self-healing within 2 years of age, it is not too late to consider treatment for atrial defects less than 6 mm and it is recommended to follow up until 2 to 3 years of age. Moreover, if the atrial defect is in a suitable position, interventional closure can be considered after 3 years of age, so there is no need to rush treatment.