Tristan had it about 5 or 6 years ago. He had to stay at the vet for 4 days!
I don't know if you feed your dog people-food or not (you shouldn't...) but definitely don't now! Only hard treats from now on also. The soft ones have a lot more fat than the hard ones. Make sure your dog food isn't high in fat either. You have to do this for the rest of his life, not just for a short time.
Besides that, just do what the vet says and give him lots of love when he gets home. He'll be beter in no time.
