Okay, Vito was shot at an age when the effect on his health could be long-lasting and quite acute. However, why'd he die of a heart attack? Hmm. Maybe it was the cat. Cat scratch fever? Maybe not. But an animal's claws or mouth are covered in bacteria that could find its way into a human body and hibernate there for years. Maybe the cat scratched him and the bacteria debilitated the infected heart muscle. Could be.