Janice,
You need to know that while Valve Replacement is Major Surgery, it is a Highly Refined Art with extremely High Success Rates (only 1% risk of morbidity and 1% risk of mortality for first timers) vs. almost certain death if he had NOT had surgery.
You also need to take comfort in that Dr. Pettersson is one of the "Best of the Best" Heart Surgeons in the World! If HE says your son will do OK, you can take that to the bank.
You also need to know that it takes a L O N G T I M E for the Heart to remodel if it was enlarged before surgery. This can be many Months to a YEAR or so. It never goes as fast as we would like, BUT, we get better and go on living our lives.
Now, as everyone has said, Get Some Rest so that YOU can be there for your son. He needs to see a POSITIVE Face from you and to know that YOU believe he will be OK. If you need some anti-anxiety medication, please ASK for it. I'm sure 'your' Doctor(s) will be glad to help.
'AL Capshaw'