Do not be surprised if he cannot play competitive basketball again. Hyprotrophic Cardiomyopathy is heavily possible.
I have it too, genetically, but really really mild. I found out from a scan in my 30s because some palpitations I thought from stress, turns out I have it very mildly. Would have never suspected, as I played sports and never had anything happen thankfully.
Now, Im told when I feel my heart racing during exercise, just take it easy, because my case is very mild.
My heart tops out at however many beats a minute, it doesn't keep going higher, like a normal person. People with normal to severe hypertrophic cardiomyopathy, their beats just keep raising and raising until it just can't beat anymore, that's what causes cardiac arrest