I can speak about this from personal experience. I had a heart attack over the summer and was admitted to one of the best cardio hospitals in Europe. I drink a large amount of coffee and asked a doctor there if that may have been a problem, and he said no. (Coffee was allowed in however much quantities you wanted it in the hospital!) Apparently caffeine itself is not too much of a risk, unless you have it by the gallon, but more the way its processed and put into energy drinks, i.e. coffee is fine and would be difficult to 'overdose' on unless you put your mind to it, but energy drinks are a nightmare. There are a few cases of students pulling all nighters to do an essay or whatever, they sue redbull to keep awake and go into cardiac arrest.
Out of interest, how many here drink carbonated energy drinks / non carbonated energy drinks before/during/after a match?
A very sad story.