I responded to you in your other thread - I wanted to respond here as well to make sure to contact you.
I am so sorry for your and your baby. While sometimes puppies can grow out of mild heart murmurs a stage 4 heart murmur is pretty bad. My vet used to have a Fox Terrier with a stage 4 or 5 heart murmur who would run all day on the farm and run with the ATV's. He did great until he was a couple of years old and then passed away in his sleep. They always considered him to be "on borrowed time" but he wasn't ever in any pain. I saw him several times (my vet's office is on his farm) and you could never tell that anything was wrong with him - he was a typical terrier.
I commend you for wanting to keep your little girl. I know how hard it would be to return her to the breeder but at least your breeder is willing to refund your money. Some breeders may put a puppy like this down but many breeders will keep a puppy instead of putting it down (please don't lump all breeders in the same basket-there are many good breeders out there as well). If you decide to keep her there may be some hard decisions to make down the road. Are you willing to do that? If not, you may want to consider returning her to the breeder. If you decide to keep her you may want to get a second opinion. I would ask about prognosis, typical life span with a stage 4 murmur, if your girl will be in any pain or discomfort, possible treatments to help her etc.
I would also talk with your breeder and explain that you have fallen in love with the girl and want to keep her and take care of her. Ask her to refund your money so that you will have the funds to take care of the puppy she bred. If you send her a vet's letter explaining the heart murmur & the answers to the above questions it might help. I know as a breeder I would appreciate a new owner being willing to take care of the puppy and would return their money so that they could.
Good luck with your puppy. I hope she does well and lives a great life with you.
Teresa |