This may be repetition, but where heart rhythm is concerned, magnesium is very, very important. Magnesium citrate or malate. If you haven't taken it before, start gently but consider pushing it to just under bowel tolerance (diarrhea). It can take months to build up your body stores of magnesium. Some people can only tolerate 400 mg; I need 1000 mg to relax properly (though I believe this will change).