I've heard Beta-Blockers referred to as "sloth in a pill" but I never really experienced that for the short time I took one. I was on metoprolol for 6 months after a bout of AFib (really, what's a trip to the Islands without a night in the emergency room?). I didn't notice too much change in how hard I could ride. I didn't notice that it helped control AFib either, so another doctor put me on Flecainide. That seems to control AFib a little better. I can still ride hard and I don't notice much in the way of side effects. I will have my 1 year follow-up for the Flecainide prescription in a few weeks.