Just ask! The us military is pretty good at helping families get to places where there family members can be properly taken care of. Just ask! it's unusual for a base to have a pediatric cardiologist, but many have connected local civilian pediatric cardiologists...
Ask EFMP. The efmp office (exceptional family member program) at your local base would have the answer.
Several. Pediatric cardiologists are on staff at many different military facilities, including walter reed national medical center bethesda, fort bragg, ft sam houston, fort lewis, tripler army medical center. Your local efmp office will have an up to date listing.
Army bases. I know that trippler (oahu, hawaii) definitely has a pediatric cardiologist. I would speak to your base physician and get referrals.