vincente I'm so sorry for your loss. I think you need to lay down the guilt you are feeling. It likely was the pain of the heart attack that caused your dog to growl and jump at the other dog the way it did. At least you were there with him at the time and did all you could. For your dog this was a quick way to go. You also did not have to make the difficult choice of having a pet put to sleep to prevent long suffering from some other horrible illness. I wish you could be at peace about this so at least you would not put guilt feelings on top of sadness. Hugs to you!