I am so sorry to hear this, I am glad they refunded your money but honestly there is no way a pup so young with a grade 3 heart murmur should have gone undiagnosed. Many pups do have "innocent" heart murmurs that they do grow out of but only time will tell, but only an ecocardiogram done when they are a little older will be able to give you the answers you seek. In the case of our heart murmur puppy Vegas/Remy, he was the largest and most robust of the litter, the vet told us that was very unusual because the pups with murmurs usually don't look as healthy as their siblings and are very small, and he got two diagnosis of a low grade 3. We were hoping this was a good sign..... and he does now live a great life with @
kim n the guys, but unfortunately it was not something he grew out of.