The clinical utility of ibutilide fumarate (Corvert) for the acute conversion of atrial tachyarrhythmias to normal sinus rhythm has been demonstrated in several randomized, placebo-controlled clinical trials. The efficacy of intravenous ibutilide for rapid conversion of atrial flutter is in the range of 50–70%, whereas its efficacy for conversion of atrial fibrillation is 30–50%. Approximately 80% of atrial tachyarrhythmias that terminate do so within 30 minutes from the initiation of the intravenous infusion. Ibutilide is more effective than either intravenous procainamide or intravenous sotalol for conversion of atrial fibrillation and atrial flutter to sinus rhythm. Age, presence of structural heart disease, gender and concomitant medication do not appear to influence the efficacy of ibutilide; however, shorter duration of atrial fibrillation is a strong predictor of successful termination. Plasma concentration of ibutilide and QT_c interval prolongation are not directly correlated with the success rate for conversion of atrial tachyarrhythmias. Ibutilide's greater efficacy compared with other antiarrhythmic drugs may be related to its ability to cause greater prolongation of atrial monophasic action potential duration relative to atrial cycle length. Termination of atrial flutter with ibutilide was preceded by increased atrial cycle length variability. Ibutilide rapidly and effectively converts atrial fibrillation and atrial flutter to sinus rhythm when administered as a 1-mg total dose followed by a second 1-mg dose. It should be used in conjunction with continuous electrocardiographic monitoring for at least 4 hours after the termination of the infusion, or until the QT_c interval returns to baseline. Hypokalemia and hypomagnesemia should be corrected before the start of the infusion. An external cardiac defibrillator, intravenous magnesium, and an external transcutaneous cardiac pacemaker should be readily available for immediate use in the event that polymorphic ventricular tachyarrhythmias occur. Ibutilide is a new intravenous agent that safely and rapidly converts atrial fibrillation and atrial flutter to sinus rhythm. (Am J Cardiol 1996;78 (suppl 8A):42–45)