I was prescribed Metoprolol (25 mg morning and evening) by an arrhythmia specialist at the Cleveland Clinic for AFIB and tachycardia.

Thing is, my tachycardia (which lasted non-stop for three weeks, confirmed by a week of Biotel Event Monitor) had stopped weeks before my appointment.

I took the Metoprolol once shortly before I went to the gym (my cardiologist said I could keep going, as my tachycardia was mostly sinus tachycardia).

It was a nightmare! I was gasping for breath when I tried to use the stair-stepper even at the least resistance (quite different from my usual HIIT exercise), even when I was merely standing. I was dizzy and faint, my normal pulse having dropped to 50, and my ordinary blood pressure (~ 110/65) dropping to 96/47.

I never took it again.

My local cardiologist said I could take it PRN (i.e., if my tachycardia returned), and if necessary at half the dose. The Cleveland Clinic MD said that was OK if my local cardio said it was OK.

So far, I have never resumed it at any dose. My pulse remains normal, only racing when I am at my most strenuous intensity on gym equipment during HIIT, dropping again afterwards the way it always used to. I have a horror of Metoprolol!

OTOH I haven't thrown the bottle out, in case that never-explained tachycardia (100-135 bpm night and day) returns.