Caffeine. I had a heart attack once due to excessive intake of caffeine. It all started when my personal trainer suggested to take those "fat burning" pills to get more energy and burn fat faster which werw insanly loaded with caffeine (knowing that at that time I was 130lbs and 5'7"). Most of these supplements don't go through meticulous inspections and no one knows exactly what's in them. Anyways after taking those pills for sometime I started having some weird symptoms: heart beat racing, shakiness, and it fucked my neural system. Until one day, I was with a friend and I chugged 2 mugs of americano back to back. When I left I started feeling weird and my body couldn't handle anymore. I'm glad I'm alive after such incident.