There are different types of heart disease. Once the disease has advanced, a low salt diet is a good idea. Prior to that it may be counter-productive. Consult your vet regarding what is best for your pet. If your dog is taking certain medication, he may need a potassium supplement. With some heart conditions, magnesium is an important element of the diet. Protein is very important since lack of it can cause heart stress. If your dog is overweight, this will put stress on the heart, so it is best not to feed him a high-fat diet. Supplements recommended for heart health include fish or salmon oil and vitamin E, B-complex vitamins, and vitamin C. Additional supplements that may help in several heart conditions include l-carnitine, taurine and CoQ10.