Metoprolol regulates heart rate. It does not regulate heart rhythm. I'm on 50mg of metoprolol, which is supposed to keep my heart rate from going through the roof if and when I have an Afib episode. The thing about metoprolol is that it depresses my heart rate all the time, not just during Afib, and as a result my HR is well below 60 BPM when I'm resting, which is technically bradycardia, and makes me feel sluggish. I had PF ablation five weeks ago and so far so good, no Afib. Hopefully I will be cleared to discontinue taking metoprolol.