as I understand it, atrial fibrillation is a disturbance of the electrical signal from the Hearts conduction system.
The magnesium you have tried may have been at an insufficient dosage to have any real benefit, as the Heart is dependent on this mineral for its proper functioning.
In addition the Heart is also totally dependent on Co-Enzyme Q10 (Co Q10) or ubiquinol-10, for its proper functioning. The body does manufacture its own CoQ10 but as we age this production can decline and especially so if the diet is lacking.
Studies at the University of Texas at Austin have shown that 75 percent of heart patients have severe deficiencies of CoQ10 in heart tissue, compared with healthy individuals.
Improvements recorded in patients given Co Q10 include increased cardiac output, stroke volume, cardiac index, and ejection fraction. CoQ10 produces an increased force of heart muscle contraction.
CoQ-10, is now a nutrient of choice in many countries. It is "routinely" given to patients with congestive heart problems in Israeli hospitals.
Japanese doctors have used CoQ-10 for cardiac problems for more than thirty years. It is now among the top six "pharmaceutical" agents used in Japan. It is prescribed for heart failure in Italy.