First of all, your dog should be on a raw diet. Commercial diets do not give dogs the nutrients that they need and this is of primary importance right now. The diet should consist of raw met and bones. No grains whatsoever.
I would also suggest that you find a holistic vet to treat your furkid. There are natural ways to address congestive heart failure. The most common cause of congestive heart failure in dogs is thought to be a deficiency in L-Carnatine and Taurine. L-Carnatine and Taurine have been proven to increase life expectancy in dogs by improving cardiac function. I would consider supplementing him with these nutrients.
I wish you my very best,