Flecainide is a class Ic drug which reduces the peak INa (sodium current), (dV/dt)max, IKr (rapid component of the delayed rectifier potassium current), IKur (ultrarapid component of the delayed rectifier potassium current). It is useful in the treatment of atrial tachycardia, atrial flutter, atrial fibrillation and accessory pathways mediated tachycardias. It reduces excitability, particularly at higher heart rate and slows conduction. This way it can block reentrant pathways.

Flecainide can also be used in ventricular tachyarrhythmias resistant to other drug, in the absence of structural heart disease. In the presence of myocardial scar it can cause monomorphic ventricular tachycardia. It can also exacerbate heart failure with reduced ejection fraction (HFrEF).

Another effect of flecainide is the reduction in delayed afterdepolarization (DAD) induced triggered activity. The drug has been used in catecholaminergic polymorphic ventricular tachycardia (CPVT).

Another important use of flecainide is for drug challenge in suspected Brugada syndrome. Ideally intravenous administration is required for the challenge. But when it is not available oral challenge has also been used. Full resuscitation team and equipment along with close monitoring is mandatory for drug challenge.

Flecainide has class IVb action as well. It blocks the intracellular calcium channel – sarcoplasmic ryanodine receptor (SR RyR2).