Flecainide-d3 is the deuterium labeled Flecainide. Flecainide is an orally active antiarrhythmic agent. Flecainide can block sodium channels and inhibit calcium ion release mediated by the cardiac ryanodine receptor (RyR2). Flecainide can be used in the research of diseases such as catecholaminergic polymorphic ventricular tachycardia (CPVT)[1].