mosely:
Even if it comes back suspect, the CAA will bend over backwards to ensure your son gets a fair hearing. They are only the regulators who dispense the rules, nothing else. They see everything in black and white on behalf of the 'system' to ensure it is fair for everyone.
Your job - if it does seem an unfair decision is to go to a reputable consultant cardiologist, preferably an AME to boot (Aviation Medical Examiner) and the best would also be a pilot. They are like hens teeth.
The good news Mosley, is that you probably live inside the catchment area of such a person! Do you live far from The alexander hospital, Machester?
If you do AND your son needs help - PM me. I've been down this very road.
Good luck Mosley jnr!