@perner

Thanks for your reply. That is very interesting as I am experiencing a similar phenomena. No problem walking 5 - 7 miles on the flats but the two 10 mile hikes in which I included some moderate climbing is where I ran into the extreme fatigue with dizziness problem after ~ 500 ft of climbing in the first 4 - 5 miles. I am assuming that I was in afib based on the input from the doctor I met on the trail last weekend but I have no hard data to back that up. I am taking double the dose of Metoprolol as you at 25 mg once a day. I will buy a heart rate monitor and use it when hiking. Low heart rate would also explain fatigue and dizziness based on getting insufficient Oxygen to the muscles and brain.

Have you considered catheter ablation to solve the afib problem?

Thanks again