I have been having the same issue with the heart rate monitor as well. When I download the logs from the health tracker, or the heart rate recorder app, my average heart rate is in the 30s. When I check my pulse with my fingers I get around 70.
What I find really weird is that when I use the WebIDE and turn the Heart Rate Monitor on manually and just watch the raw data on the event my heart rate eventually reads 70 BPM after a few moments.
I am also on 2V12. Not sure why my logs are so low.