Low Heart Rate...?

I am 2 years post op and have lost 170 pounds.. I have a very low heart rate..? Resting it is 42-46 beats per minute... Anyone esle have this problem... The doc's seem to thing that because I have lost all this weight that my heart doesn't have to work so hard now...? They say people that are very active, have low resting heart rates... I am very active but not like a cardio instrustor...?