I agree with the others. You need to talk to a veterinary nutritionist who is experienced in treating animals with cardiac problems. I personally use Dr. Rebecca Remillard for home cooked food options. She is at North Carolina State University now. I also know that Dr. Lisa Freedman at Tuft's university in Boston has an interest in cardiac issues so she might be the best nutritionist for you to talk to. Here is a link to her profile
Faculty and Research : Cummings School of Veterinary Medicine at Tufts University