Sematilide is a class III antiarrhythmic agent and an analog of sotalol .1 It prolongs electrically stimulated action potential duration (APD) and increases the effective refractory period (ERP) in isolated guinea pig left atria. Sematilide decreases spontaneous sinoatrial beating rates and induces ERP prolongation of the atrioventricular node in isolated perfused canine hearts.2 In situ, sematilide (1 mg/kg) increases ERP, prolonging cardiac refractoriness, in open-chest dog hearts. Sematilide (0.3-6 mg/kg) inhibits arrhythmias induced by programmed electrical stimulation (PES), but not coronary ligation and reperfusion, two-stage coronary ligation, adrenaline, or digitalis, in dogs.3 Formulations containing sematilide have been used in the treatment of arrhythmias.

References
1. Ishii, Y., Muraki, K., Kurihara, A., et al. Effects of sematilide, a novel class III antiarrhythmic agent, on action potential in guinea pig atrium. Jpn. J. Pharmacol. 68(2), 175-182 (1995).
2. Yamada, A., Motomura, S., and Hashimoto, K. Comparison of direct negative chronotropic and positive inotropic effects of sematilide to those of E-4031 and MS-551 and the reverse frequency-dependent prolongation of cardiac refractoriness of sematilide. J. Cardiovasc. Pharmacol. 27(1), 159-166 (1996).
3. Xue, Y.X., Eto, K., Akie, Y., et al. Antiarrhythmic and proarrhythmic effects of sematilide in canine ventricular arrhythmia models. Jpn. J. Pharmacol. 70(2), 129-138 (1996).