Azimilide is an investigational Class III antiarrhythmic that has been developed for treating both supraventricular and ventricular tachyarrhythmias. Similar to other Class III antiarrhythmics, azimilide prolongs myocardial repolarization in a dose-dependent manner by increasing the action potential duration, QT interval, and effective refractory period. The most frequent reported side effect is headache, with rare serious adverse events of early reversible neutropenia and Torsades de Pointes. In long-term follow up, the patient withdrawal rate has been low. Azimilide has very predictable pharmacokinetics, is predominantly hepatically metabolized, and has no significant drug interactions with digoxin or warfarin. In animal models, azimilide has been shown to be very effective in suppressing both atrial and ventricular tachyarrhythmias, decreasing the defibrillation energy requirement, and preventing post-myocardial infarction ventricular tachycardia and fibrillation. Clinically, in a series of 4 double-blind, randomized, placebo-controlled trials, the Azimilide Supraventricular Arrhythmia Program which included over 1000 patients and approximately 70% with structural heart disease, azimilide showed a significant prolongation in the time to first recurrence of paroxysmal supraventricular tachycardia or atrial fibrillation / flutter. With respect to ventricular tachyarrhythmias, the AzimiLide post-Infarct surVival Evaluation Trial was a large randomized, multinational, prospective, placebo-controlled study in recent survivors of myocardial infarction at high risk for sudden cardiac death. After 1 year of follow-up, this study showed no statistical difference in all-cause mortality between placebo and azimilide. However, azimilide did statistically reduce the incidence of new atrial fibrillation. Further trials are necessary to evaluate the efficacy of azimilide in patients with symptomatic ventricular arrhythmias.