For 1/3rd of all heart attack victims their first symptom is sudden death.
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One doesn’t have to be old either. It happened to my 33 year old son-in-law. Died in his sleep.
I lost a good friend that way. Died playing basketball, 43 years old. No warning, worked out regularly, weightlifter. He had sown some wild oats in his youth, done some drugs, including some steroids, which I suspect may have contributed.