A decrease in appetite, also called anorexia, is a common occurrence in animals with declining health, not just heart disease. In dogs and cats with heart disease, loss of appetite can be due to heart failure, side effect of one or more medications, an abrupt change in diet, worsening kidney disease, or other diseases unrelated to the heart. A blood test is needed to determine whether the problem might be due to worsening kidney disease or electrolyte disturbances.
Certain medications are more likely to be associated with a reduced appetite, so check with your veterinarian to decide whether or not to try a reduced dose of one or another medication—discontinuation of the incorrect medication can lead to worsening of heart failure. In some animals, changing the diet or supplementing with fish oil can help restore the appetite.
More diet information and tips on how to keep your pet interested in food can be found in the Diet section.