A physically normal person w/ healthy heart w/o higher sensitivity to caffeine who consume it in moderation don't. It's like saying this person eats strawberries and dies, therefore strawberries are poison. No, the person had allergies or consumed it in excess. Or it's like putting poison label on water bottles because someone drank 4 liters in matter of a few hours and had water intoxication and died. You can kill anyone if you feed excess amount of any substance to them. If caffeine resulted in fatal arrhythmia in average populationwide, I don't think we would have coffee shops in every corner. You'll always have people w/ conditions and/or allergies to any substance that general population tolerate well, though we can't label substances as position based on how minority of population react to them.