When 38 years old, I was at work, started getting pins and needles in my hands, sweating like a sweaty thing sat somewhere cool and it passed, drove home it started again, passed out at mothers woke up in an ambulance hooked up to several machines, whisked into local emergency dept and monitored for a couple of hours, then had another one so whisked from Weston super mare to Bristol heart unit in sub 20 minutes, 4 days in hospital, lots of tests, including exercise test, passed easily.
Blood test showed minimal salt in my system which caused the heart attack, took about 4 months to recover, was banned from bikes for what seemed an eternity.
Over exercising and not enough food, was training for Kielder 100 at the time, doing 75mile SS ride on weekends and 4 other nights training during the week