@713j I know a man on afibbers.org who doses himself with as much as I gm daily via a concoction he makes (Mg water). Since you don't really know where you are at baseline, unless you DO know (you haven't said that you are definitely deficient), I would take no more than 400 mg for a few days and see what happens. This is not advice...I'm saying that it is what I would do if I had no other information, was experiencing an arrhythmia, and wanted to experiment with Mg supplementation. To be safe, you should consult an electrophysiologist or a cardiologist.