Your best bet is evaluation by a veterinary cardiologist at a veterinary teaching hospital, referral clinic or a veterinary medical school. There are no
veterinary medical schools
in South Carolina. The closest is
in Athens, Georgia, and Raleigh, North Carolina. I don't know if these areas are too far for you, but your vet should be able to send your dog to a referral clinic with an attending veterinary cardiologist close to you.