I too take metoprolol tartrate* PRN (half of a 25 mcg pill). That's for AFIB when I have tachycardia too ( detected through my Apple Watch). It is seeming that working out in the gym - weights and some aerobic exercise - often precipitates the tachycardia. It's as if the increased heart rate from aerobic exercise is just taking a very long time to return to normal. (Lately, up to days. Once, two weeks!)

I also often have a terrible night's sleep afterwards which seems to amount to not just tachycardia but AFIB - apparently the whole night. A sleep app with the Apple watch records my sleep rate . (BTW, AFIB prevents my sleep; at least, it keeps me from anything but a light, unrestful sleep.)

Also, after such a night (it's happening today, for instance) I have been having episodes of extreme dyspnea - breathlessness. A few hours ago, after climbing one flight of stairs (usually a breeze) I barely made it to my bed to "catch my breath". I had to lie there for a good while.

Wondering if the solution is to take the metoprolol more often or this other medicine being discussed - Atenolol. And what about the workouts? (I have been previous told by my cardiologist that this regular exercise is important for my cardiac (and other) health. (I'm almost sedentary otherwise.)
Besides, I guess "everybody knows" exercise is crucial for health and longevity!

*Anyone know the difference between Metoprolol tartrate and, um, the other kind?