I'm so sorry to hear this! I lost a 12 year old Sheltie to congestive heart failure 5 years ago. Having been through this, the one thing I can tell you is that the drugs available to treat this are great. My boy was old when the problem was found, so the odds were stacked against him. Because of the age of your dog, I think you will be able to manage the condition with meds, special food, good vet care, and he will live to be a senior dog. Best wishes.