Something to think about on this: Dogs have short lives, like 12 to 15 years. How many people have heart attacks at or before that age? Not many. A heart attack is usually a clogged artery from a build up over times of cholesterol or other blood products that are not processed out of the body. Dogs don't have the time for that to happen. There might be other reasons that dogs don't get heart attacks, however. I read somewhere that dogs, and some other animals, manufacture vitamin C in their bodies, and it makes for a vitamin C amount in them like 20 times what humans have.
I was not too happy about the experiment of trying to tie off a dogs arteries so as to induce a heart attack in him. I am for research as much as the next person, but if you tie off enough arteries in a dog you will kill him. What did you learn? I think better would be to feed the dog human food and not let him exercise. Then you will get a dog you can study for clogged arteries and who will be a potential heart attack victim.