An atrial septal defect of 10 millimeters is considered medium-sized. If it's a primum atrial septal defect, surgical intervention should be performed as early as possible.For secundum atrial septal defects of this size, since the condition progresses relatively slowly, noticeable symptoms and pulmonary hypertension or heart function decline typically don't appear early. Therefore, surgical treatment can usually be postponed until preschool age.There are two treatment options available:1. Interventional closure surgery2. Open-chest surgeryBoth of which are definitive treatments. However, primum atrial septal defects can only be treated through open-chest surgery.The surgical approach may involve a right subaxillary incision to access the chest, establishing cardiopulmonary bypass and using a patch to close the defect.