As to whether he would,
in fact, be allowed to play contact
sports with a bioprosthetic valve
in place, I am pretty certain that there would be a waiting period of at least about a year, to make sure that the sternum was fully healed. After that, I'm thinking it would probably depend on the policy of the institution for which your son wanted to play. If they say no, then he won't be playing, and I don't believe there is any universal rule about it.