My hubby was having palps at increased frequency and decided it had to be diet soda because of an article he had read. All along I was pretty sure it was caffeine since we know he's very "drug" sensitive. He went off both and then one day drank two diet sodas and had them again. Here's the funny part... he was so happy to be able to tell me he was right, then I looked at him and asked if he thought it could possibly be the 1/2 box of thin mint girl scout cookies he ate earlier (chocolate)!! He laughed and was willing to consider it might be the chocolate. Long story short, with him it's very chocolate and caffeine related but you need to have it checked out. I actually have been uncomfortable at how little concern his doctor showed.