Abnormally Low Heart Rate

  I recently went to the doctor - and in the course of the exam learned that my pulse rate (confirmed by EKG) was stightly below 40 beatds per minute.  I had come in with complaint of insomnia - i.e. - no problem falling asleep but awaken before 4:00 AM and unable to fall asleep for normal # hours.  I am in early 50's, and over past two years have lost 65 lbs, on a very strict low fat (restricted calorie) diet, and
  an exercise program - running five times per week, some weight training (after having been a lifelong couch potato!).  Blood tests had not shown abnormal thyroid readings - and if anything I feel stronger, and more energetic then I did prior to starting this diet/exercise regimen - i.e. I do not feel weak - which I understand is a symptom of bradycardia.  Question:  does this need to be investigated further, or should I just forget it?
---------------------------------------------------------------------------------------------------
Dear Joyce:
Many athletes (especially runners) have low resting heart rates.  As long as the EKG shows a normal sinus bradycardia, and as long as the heart rate rises appropriately with exercise, there is usually no problem.  A low heart rate can sometimes cause dizziness or lightheadedness, in addition to fatigue, but this does not appear to be the case with you.  An underactive thyroid can cause a low heart rate.  Sometimes electrolyte imbalances can cause a low heart rate and this is of particular concern if someone is on a very restrictive type of diet.  
Information provided here is of a general nature.  Specific diagnoses and treatments can only be made by your doctor.  If you would like to be seen at the Cleveland Clinic, please call 1-800-CCF-CARE for an appointment with a cardiologist at Desk F15.

[tebba]

A related discussion, runner's heart rate was started.