my daughter was born with aortic valve stenosis
and has just had the Ross procedure done.
She loves fast rides and she specifically asked her cardiologist about this: he said she could go on fast rides as her heart is ok at the moment and he thinks rides should only be avoided with conditions that effect the electrical functioning of the heart.
Please don't take my answer as conformation though. The safest thing to do would be to ask your sons cardiologist.