Shannon, I know this is difficult for you but these are good hospitals and I'm sure they do this sort of thing fairly frequently. There is always the Cleveland Clinic, too, another terrific hospital. We are blessed to have this care available to us.
My father had his aortic valve replaced back in 1971 with an artificial valve! It was pretty much experimental back then but Dad needed it done or he wouldn't survive. I was sooo frightened but he came out of it with flying colors. So, just imagine the strides they have done in the past 39 years when it comes to heart surgery! I really feel your son will be just fine.
Of course, I will be praying for you, your son, and your family. You know that God is in control so try to lean on Him and not carry the load yourself.
Sherrine