Hi Welcome to health care magic. You have enumerated good reasons to give magnesium as you have mentioned, it is cardiac muscle stabilizer so prevents against arrhythmias and it is important to replace magnesium in alcohol abuse people because they have decreased intake in the diet so are Mg depleted. Cardiologists and general care doctors prescribe it for increasing the gut motility and for producing soft stools and to prevent straining at stools particularly in cardiac patients. I hope the advice will be helpful for you.