I'm doing the same -- riding 50 - 60 miles a weekend. Although it's only been a few months, it's amazing what it will do for you !
I recently took a physical for a new insurance policy. I had to fast overnight, and at 8 a.m. the next morning the nurse came to the house to take all the vitals. My sitting, at rest heart rate was 46! She had to take it again. She said she had never taken someone's heart rate at that low a rate that was not sick or something. I have had it at 43 BPM also. Before, when I was fat, it was about 80 or 85 BPM. Just shows how hard your heart is working when you are overweight! You can test yours by taking your heart rate when you wake up, before you start moving around. See what your sitting heart rate is. Then make sure you use a heart rate monitor when you ride and watch that baby go crazy as you pound the hills! Good luck. Watch for fenders!!! ;^)