Have been dealing with CFS for last 4 yrs. PEM is the biggest problem and has a threshold of walking for around 7 mins. Either walking or doing any physical activity the first symptoms i feel are the increased heart rate and lightheaded. My primary doctor suggested me to consult my cardiologist to prescribe beta blocker( either propranolol or Zebata) to reduce my heart rate. Basically to test if reducing my heart rate with medication will help increase my physical activity threshold. Would like to know if any one has tried these meds and will reducing the heart rate help in increasing my physical threshold? PS: I was tested and don't have POTS.