About 2 years ago, I noticed that my heart was beating irregularly and very hard at times. Im only 21, very active, bike everywhere and don't really smoke (only occasionally and socially) or drink heavily. My resting heart is often 120 and sometimes it drops down to around 80 but it never goes below that. I do not have chest pains and have never passed out and have no trouble exercising. (I just did a 140 mile bike ride without training and felt fine. I have never felt weak except when my doctor put me on beta blockers for several months, not to mention all of the other unpleasant side effects they come with. They actually made my quality of life worse so I got off of them. Im starting to get worried about this because I have been to several cardiologists, even to Stanford and not one of them can even explain or offer suggestions to what may be causing this. Ive also been to an endocrinologist and had my hormone levels and thyroid tested it came up normal. I even got tested for lyme disease because I was having joint issues and some symptoms that matched and it came up negative. A heartbeat of 120 may work out for me now because im young, but i know it is by no means sustainable once I get older. It is really discouraging when the some of the best doctors are confused themselves and are of no help other than trying to make me take drugs. At this point I dont know what to do and any suggestions would help. thanks