Energy drinks are soft drinks advertised as providing energy to improve physical activity of the drinker, as compared to a typical drink. Rather than providing food energy (as measured in calories), these drinks are designed to increase a user's mental alertness and physical performance by the addition of caffeine, vitamins, and herbal supplements which may interact to provide a stimulant effect over and above that obtained from caffeine alone.
Well, I've never tried one. They're sold here in Mexico, I drink coffee though.
Coffee's the same thing, Marcos, IMHO.
The caffeine squeeeeezes your veins, making your heart pump more.