It is possible to have “a heart attack” and not know it. My father apparently suffered his first at around the age of 50, but passed it off as “a bad weekend”, when he came home from work one Friday night feeling awful, and spent most of the weekend in bed. (Which was highly unusual for him.)
Some time later he had an accident at work where he lost his balance in stepping down from a height of a few feet, fell and injured himself. He was taken to the hospital for the injuries from the accident and as part of the ER treatment – and apparently because of the way he said he had felt at the time he lost his balance – he was given an EKG. The attending physician asked him for the name of his cardiologist to follow up with, and was surprised that he had never been examined for cardio problems. Apparently he could tell from the results of the test that the immediate cause of the loss of balance was a “significant” heart attack, but it also indicated that there had been damage from an earlier event, too. Dad had no idea; up to that time he had never had an EKG or an indication of heart problems.
After he started to receive specific cardiac care, the cardiologist was able to deduce from the account my Dad gave him that the earlier “bad weekend” had probably been the initial cardiac event. So “mild” heart attacks can occur and be passed off – but Dad had also been in exceptionally good shape for a man of his age, too, which probably helped, of course.
And in one respect, @Hawaii_Jake may be incorrect: My understanding is that all heart patients die, not just a third of them. But so do Olympic athletes, presidents, kings and poets. You just can’t win. I’m planning to live forever. So far, so good. There’s a first time for everything, right?