[Evans, Marv]

I'd sort of agree with Slodave's comment. I don't think your altitude can have anything to do with it though. I used to have a heartbeat in the mid 40's aftewr I worked & lived in the mountains at above 8K ft. & up to 12K+ ft. for 3 to 4 months. However, that was a result of living at an altitude where the partial oxygen pressure was low. That caused my red cell count to go sky high to compensate for the lack of oxygen and resulted in a reduced heart rate when I went to a lower elevation.