I would get to vet if throwing up bile and not food then stomach is empty. Have you tried soaking food he normally eats as chicken may be a problem for dogs that have ibd (food intolerance) another thing you could try is food processing the chicken with rice so easier to digest. So sorry you are going through this
There is a good article in the whole dog journal you can purchase individual articles and it talks about getting seniors to eat and how they recommend. Some times they have to do steroids to increase appetite as well but not sure how steroids and heart disease will work. I would go to vet and get a senior panel done asap
there is a recipe to get dogs to eat called satin balls if you google it there are a ton of dog groups that have the recipe. Also the medication could be making him not hungry as my friends yorkie had this happen- did they change the meds recently?