Marci - I wanted to post - because tonight as I was getting a book to read to Em for her bedtime story I came across her "heart books". I think Em is a lot older than your son (she was 6 when she had her last surgery but developmentally more like 4ish) I don't know how old your son is or how much preparation you are planning to do with him if he needs heart surgery, but I have some fantastic books that helped Em so I thought I would share the titles and if you're interested you can see about getting them.
* "Matty's Heart - A Child's and Parents' Guide to Open Heart Surgery." I love this one it has lot's of pictures and explanations - I don't read all the words to her (some of it is a bit deep) but I talk to her about it.
* "Matty's Heart Cath - Story and Coloring Book" (I'm not sure if your son would need a cath if he has surgery but this is a good one too)
(I purchased both of those books - as well as several others- from
KIDSWITHHEART.ORG)
* "Do I have to Go to the Hospital? A first Look at going to the Hospital" by Pat Thomas
And then I think we also read a Berenstein Bears go to the Doctor and Curious George goes to the hospital and another one I can't think of when she was 3 and had her surgery.
Some of the heart books, even though they are children's books, really helped ME. It makes it very easy to understand in non-medical language. I don't speak "doctor" very well. I also recommend "It's My Heart" from the Chidren's Heart foundation. It's a resource guide for parents of kids who have congenital or aquired heart disease.
Hope everything is going well for you and your son!