Dear Ambhika,
A ventricular septal defect (VSD) in the subaortic area is MOST LIKELY the same as a perimembranous or conoventricular septal defect (though not always). If your cardiologist says that this is the same as a perimembranous VSD, then the following applies. Since the defect is small, it is not causing any problems with the function of his heart or lungs. However, because it is below the aortic valve, the jet of blood going across the defect can cause the aortic valve to deform and to leak over time. There is a small chance that the defect will spontaneously close, but it is likely not to. He will require lifelong surveillance of his aortic valve as well as the defect to ensure that the valve is not being inappropriately deformed. Beyond that, there are many many people who have these small defects and, other than a very slightly increased risk of an infection of the heart, have no problems throughout their lives. It will be important to ensure that he has good oral hygiene lifelong.