is a class IA antiarrhythmic that works by blocking sodium channels in the heart. This causes slowed or blocked conduction; decreased slope of phase 0 depolarization; increased action potential duration, effective refractory period
, and QT interval. The effects are state dependant, tissue that frequently depolarizes will be selectively suppressed. Procainamide is commonly used for atrial and ventricular tachyarrhythmias, and especially for re-entrant and ectopic supraventricular and ventricular tachycardia
. It is often the drug of choice for Wolff-Parkinson-White syndrome
. Procainamide can cause a reversible SLE-like syndrome that gives anti-histone antibodies in the serum.