It's common sense - for dogs and people - that a lean, healthy diet is good for the heart. It's also common sense that an excessive, unbalanced diet is bad for the heart.
Your dog's diet needs to be balanced and made up of high quality ingredients that meet its nutritional needs. These needs can change depending on your dog's age and state of health.
Talk to your Vet about how much and what type of food you should feed your dog.