The fact that they took your child off the Lasix and
Digoxin is a very good sign, especially if he is gaining weight, albeit slowly, without it. And without signs of heart failure like sweating or tachypnea, those are also good signs that he's fine to wait. While a VSD repair is probably one of the easiest OHS repairs, there are still very real risks, and if your son is in a stable state, then he is far better off postponing surgery.