Sematilide hydrochloride（Cat No.:I009431）is a class III antiarrhythmic agent that selectively blocks cardiac potassium channels, prolonging action potential duration and refractory periods. By inhibiting the delayed rectifier potassium current (IKr), it stabilizes cardiac rhythm and helps suppress reentrant arrhythmias. Investigated for use in atrial and ventricular arrhythmias, sematilide showed efficacy in reducing abnormal excitability, though concerns over proarrhythmic risk limited its clinical development. Supplied as a hydrochloride salt, it offers stability and solubility for laboratory use. It remains a valuable compound in cardiovascular and electrophysiological research.