Hi.. ASD are usually asymptomatic and do not need any treatment if the size of the defects is small.. 10mm defect is fairly large defect. However if he does not have symptoms now, you may wait for the time as suggested by your doctor for it to close.. It is quite possible that this will close over a period of time.. Even partial closure is ok to prevent surgical treatment. He will be able to have a normal life with minimal defect.. So it is not a bad idea to wait and see, then subject him to a surgical treatment now, taking into consideration that he does not have any symptoms now..