I have Diltiazem for this purpose. This is a calcium channel blocker. Since my a-fib rate isn't that high and is pretty manageable, I will usually wait about an hour to see if it corrects on its own. If not, I take a 30mg dose, which often seems to encourage sinus rhythm. I have been authorized to take up to 120mg, but would never do this, since I have a low heart rate in general and Diltiazem depresses the rate further when I take it. My episodes occur about once a week.