mystery tachycardia

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

[PDee]

I had a similiar experience a couple of years ago resting heart rate (first thing after sleeping) around 115-120.  The whole "take beta-blockers because we really don't know whats wrong with you".  My thyroid was "fine" but I decided to go into a local clinic a have my thyroid tested again. Suprise, suprise. My TSH was actually out of range.  Since then I have had my thyroid antibodies tested (not all doctors will want to do this) and these came back extremely high.  So at this point I am waiting for another appointment with an Endo.  I would ask to see the results of your "normal thyroid" test and then start doing research. There are many different kinds of thyroid tests that all show a different portion of the thyroid puzzle so also find out which tests were done.

[mista_sniff]

Thanks.  Im supposed to meet with the cardiologist soon so i think I will ask to be tested again by an endo.  Are you still experiencing the rapid heart rate?  Ive heard of things like this that eventually clear up later in life but who really knows.

[PDee]

I still do have the tachycardia. How's your bloodpressure?  Mine is usually very low even off BetaBlockers (will make me light headed sometimes) not sure if this is normal with Tachy or not.  I hope that now the doctors see that my thyroid is off they will treat me and this could help get my heart rate under control.  

I think it is usual for childrens heart rate to be higher than an adults anyway maybe it takes longer for some of us to grow out of this.