I have the same problem w high heart rate. Things that help me: 1) Laying down like a mad person wherever/whenever if it goes over109, pharmacy, i don't care I go horizontal. The more I avoid going aerobic the better over time it gets. 2) I have tried supplements and monitored HR, the best so far to lower is MB12 and Olive leaf extract (taking them the moment is high). 3) Pedialite, If I keep hydrated less HR variability. 4) Food, I check my HR as I eat, if HR goes up too much while eating certain foods, then I avoid, Example: Rice, Whitebread... 5) Exercise. I get PEM so only do stretching (a few minutes) and next day I get better reading.