Attitude. All important, as has been said. I'm not a medico, but I, too, have a bad valve resulting from scarlet fever as a kid. 30 years ago I found an oil slick on my motorcycle and broke every bone in my right let, and the tibia and fibula (in two places) on my left. Within 24 hours I was comatose from a fat embolism. We can argue about why I'm still here, but the doc's opinion was that I was in very good shape, had a good attitude, and those were the key. I've worked hard since, keeping myself healthy.
Keep us advised as to how things are going, and know your son and family are in my thoughts.