Sick animal sold

Bought a Long Hair Chihuahua puppy at Darling Pets on Broad St. in Rome Ga, had it a week and took it to a Vet and found it had a heart murmur. Called the pet store to try to work out a refund on the don so that I could keep the dog and have the necessary surgery to fix the problem. The pet store owner said that unless he takes the dog to "his" vet and had it diagnosed he would not refund our money and he would have to keep the dog. I told him that we would have a vet from the University of Tenn @ Knoxville school of veterenary medicine to give a second opinion and perform the surgery and that we would submit both diagnoses and the medical record from the surgery if he would provide a refund. He refused. I will not return the dog to the pet store only to have it put down. The pet store owner said he would give our money back if we would return the dog but he would not allopw us to keep it. The vet stated that the ouppies medical problem was hereditary and that the parents would also have the condition and that the dogs breeders would know that they were supplying defective puppies to pet shops. The puppy is also registered with the CKC and shouldnt be. is there no law to require a pet store to have a dog examined before it is sold? Thank you.