Puffinstar, I had my first heart attack at 35 years of age, my second heart attack at 40 years of age, and at 46 had two stents put in for 80% blockages. I'm still able to live a fairly normal life, although my heart is no longer very strong.
Make sure your son takes this as a sign and changes any behaviors that may have brought it on, i.E smoking, fatty diet, stress. His chances of living a normal life are hopefully good, but he has to realize that his life will be different. Some negatives i've been faced with are not really health related. Getting life insurance is impossible, getting health insurance is very difficult, and getting hired by someone who knows my past history (or requires a physical) is impossible.
I'll be glad to help answer any questions or concerns you have.