I know someone (also in his early 50s) who was driven to hospital by his doctor wife after experiencing vague chest pain and other non-specific symptoms. He didn't know he was having a heart attack. His heart stopped while in the ER waiting to be examined, and she resuscitated him herself. His survival (with no impairment) was dependent on his wife recognising the signs of the heart attack, and getting him to a hospital in time, and being a doctor. I suspect that in that sort of situation, luck plays a big part.