My cardiologist recommends Magnesium Glycinate. I take Nature Bell 500MG caps along with Pure Mag. Glyc. 120MG caps after breakfast. I take another Pure 120MG cap after lunch. That split dose is fine with my Dr. but you should check about the amount you should be taking. Some folks can get diarrhea from high dose Mag.
I also learned from this website that there may be some connection between a-fib and gut health so I take a probiotic by Thorne called Cagulans Baccilus-2 caps daily (split dose).
Good luck!