To date, only one prospective, randomized trial has compared the effectiveness of a calcium channel blocker (diltiazem) with a beta-blocker (metoprolol) for rate control of AFF in the ED. Despite the relatively small sample size (n=20 in each group) the authors concluded that both pharmacologic agents were similarly effective. In order to test this finding, the investigators conducted a prospective comparison of metoprolol and diltiazem for the management of patients presenting to the ED with AFF with rapid ventricular rate.