I don't think there's long term evidence for negative problems. However, high dosages of caffeine are dangerous and have killed people. Those dosages are easily achieved through the likes of energy drinks.
> And easily achieved through energy drinks?
Yeah, once you start pushing 1000mg of caffeine, you are getting into areas where if you have heart problems, you could be putting yourself in danger.
> Most energy drinks
But not all. So why strongly doubt it?
There are plenty of energy drinks which are fairly popular with huge amounts of caffeine and there's little labeling requirements to let people know that. Bang energy drink is a good example of that. 300mg per can, meaning 3 cans is putting you in dangerous territories.