i used to take protein shakes to go with my workouts. gradually i found myself havving a racing, thumping heartbeat. i couldn't understand what was causing it, never even crossed my mind that it could be the protein drink. then one day i read through the ingredients and found that it contained taurine, also an ingredient in red bull and the like. i stopped drinking the shakes and my heartrate quickly returned to normal.
after a drinking session your heartbeat will already tend to be racy, drinking redbull will only exacerbate this. really, the best source of energy (and in my case protein) is a proper, sensible diet and keeping yourself reasonably fit and healthy. if you need an energy drink to get you going then you probably have a deeper problem.
