I am sorry to hear about your grandson.
My first (and so far, only) grandchild was born in January 2003 with Transposition of the Great Vessels.
The first 2 weeks of his life was one of the most terrifying periods in mine.
He had open heart surgery at 10 (11?) days old and is now healthy, happy, normal toddler. Please, feel free to pm me anytime you need to talk.
As far as congenital heart defects go both Atrial and Ventricular septal defects are fairly minor. They can often close on there own as the baby grows.
Whether or not the defect needs to be surgically repaired depends on the severity of any symptoms. The surgical procedure is pretty straight forward but does require open heart surgery and all of its associated risks.
Thanks to the amazing resilience of children they bounce back MUCH quicker than adults do.
Once you know exactly which defect your grandson has I recommend the following sites: