I am so sorry for what you and Molly are going through. I have a six month old puppy who was diagnosed with dilated cariomyopathy when she was 4 months old, so I know how difficult it is to receive news like this. We were told that dogs with this type of heart condition usually live six months to 2 years, however, we are doing everything in our power to ensure we have Belle for a long, long time. We were told the same thing by our cardiologist, to just let Belle be a puppy and enjoy her life. They told us that Belle would limit her activity herself. For the most part, that is what we do. We have made some concessions to Belle's illness, like I don't put both of our dogs into the back yard at the same time because I know they will run like crazy. I also break up the wrestling matches the dogs have when they get too wild.
We are going through a difficult period right now with Belle. Last week she went to the vet for routine bloodwork and they found a pretty significant arrhythmia. The cardiologist changed her meds, and she had more bloodwork and an EKG on Friday. She still had a significant arrhythmia. Once again they changed her meds, however we ended up back at the vet's today because I was concerned Belle wasn't acting like herself. The arrhythmia is persisting, but the vet thinks we haven't given the meds enough time to work. One of the things I have found is that because Belle is growing so much, it is more difficult to regulate the dosages of her medications. I am saying my prayers that this arrhythmia stops, and that we are once again on an even track. So sorry I have been rambling on....
Remember, be strong for your girl. Do what the doctor tells you, give her meds at the same time everyday, and just love her to pieces.