I imagine your dog is on a low-sodium diet, or perhaps a prescription diet. I do not know how severe your dog's heart failure is, but recent research has shown that some sodium might have some benefit in subclinical heart failure. Look up the human study "Normal-sodium diet compared with low-sodium diet in compensated congestive heart failure: is sodium an old enemy or a new friend?" Of course, high-sodium foods like human snack foods, cheeses or cold cuts should be avoided, as these cause a sudden spike in sodium levels. Consult with your vet about your dog's difficulties with eating. He or she may suggest appetite stimulants or another type of food. Some dogs do better with canned food. If you are feeding him dry, see if the brand you use also makes a canned version that you can mix in with the dry. Although it may be ideal to eat a cardiac prescription diet, your vet may be able to suggest another high-quality diet. That or you can ask a vet specializing in nutrition for a recipe for a balanced diet that you can prepare at home.