Very fast, unpredictable heartbeat

My heartrate has recently been unusually high at rest, and sometimes fluctuating.  It has recently been around 100-130bpm, but on one occasion was 155bpm.  However, on another occasion it was 53bpm!  My heartrate used to always be around 50bpm at rest.  I am 20 and do a lot of exercise/sport.  I have also been having palpitations.  My doctor gave no insight as to what this could be.

Many thanks for yor help.

[Michael J. McWilliams, M.D.]

You need to see it on a rhythm strip.  It is likely a normal rhythm that is fast (sinus tachycardia) but you need to see it to know for sure.  A monitor should also help diagnose the cause of your palpitations.

Any treatment would be based on what they find on the monitor.  Thyroid studies are usually checked in this situation to make sure it is not over active.