Dofetilide is an antiarrhythmic drug with Class III (cardiac action potential duration prolonging) properties and is indicated for the maintenance of normal sinus rhythm. Dofetilide increases the monophasic action potential duration in a predictable, concentration-dependent manner, primarily due to delayed repolarization. At concentrations covering several orders of magnitude, Dofetilide blocks only IKr with no relevant block of the other repolarizing potassium currents (e.g., IKs, IK1). At clinically relevant concentrations, Dofetilide has no effect on sodium channels (associated with Class I effect), adrenergic alpha-receptors, or adrenergic beta-receptors. The mechanism of action of Dofetilide is a blockade of the cardiac ion channel carrying the rapid component of the delayed rectifier potassium current, IKr. This inhibition of potassium channels results in a prolongation of action potential duration and the effective refractory period of accessory pathways (both anterograde and retrograde conduction in the accessory pathway). Used for the maintenance of normal sinus rhythm (delay in time to recurrence of atrial fibrillation/atrial flutter [AF/AFl]) in patients with atrial fibrillation/atrial flutter of greater than one week duration who have been converted to normal sinus rhythm.