I had or at least I thought I was having problems with my heart at one time also...It is a very scary thing. Mine wasn't activty related though, so this probably won't help....I would be at work, and my heart would beat so fast I thought it was going to beat out of my chest, beating really fast, fast enough to make me a little light headed.....I assumed it was an anxity attack....It kept happening....I went to the Dr after a couple of days, and he told me that it was caused by stress and too much caffine, because I drink an exess of coffee in the mornings......He told me to reduce my stress level, (which can't happen) I have decreased my coffee intake, though....He told me to just try and ignore it....and it would go away...(That is a little easier said than done) and it would go away.....It did go away for the most part, but it still does happen from time to time, but not like that time which lasted almost a week. I do suggest if it continues to happen to get it checked out, its better to be safe than sorry.