Most of us have HR less than 75 when at rest, but the medical community seems to think that anything less than 100 BPM is considered within 'normal' range. There are others in the medical community, and I share their view, that anything higher than 90 BPM is a sign that something is going on. Personally, and it's just my opinion, and I have been a fit runner all my adult life (with resting HR of 38), when I awaken to a heart at 70BPM, I figure I'm in slow AF or I'm having PACs (premature atrial contractions). A recent Holter monitor confirmed the PACs. When my Samsung Galaxy watch shows HR of 85, I know I'm in AF. Above 120 BPM, I'm in flutter.
You are allowed up to 200 mg of metoprolol each day ON THE ADVICE AND UNDER CARE OF A QAULIFIED PHYSICIAN!! I just came off 150 mg when a second ablation seemed to have fixed me. Months earlier, a week after my first ablation, I went into tachycardia and was put on amiodarone. I had to cut the metoprolol the same day...cold turkey. Didn't phase me because the nasty and toxic amiodarone cured my arrhythmia...oops...STOPPED my arrhythmia. There is no real cure that we know of. My point is, metoprolol works, but some don't tolerate it well. More may actually be better. You want your HR lower than 100 consistently, and if you can get it less than 80, that's great.