My son did not pass his physical, the doctor said he had a double heart beat, with a low heart rate.what could be the cause?should i be worried?

Depends: it is not unusual for an athletic male 14 year old to have a low resting heart rate, this often is normal. "Double Heart Beat" could be a "premature ventricular contraction" which occur normally in teens, and can be heard on exam. I am concerned that you have these lingering questions following your evaluation! Follow your doc's recommendations for evaluation. Don't worry, but pursue answers