Procainamide (Pronestyl, Procan, Procanbid) is an antiarrhythmic used for cardiac arrhythmias, classified as class Ia. It is a sodium channel blocker which blocks open sodium channels and prolongs the cardiac action potential (outward potassium (K+) currents may be blocked). This results in slowed conduction, and ultimately the decreased rate of rise of the action potential, which may result in widening of QRS on electrocardiogram. It is a hapten. It is metabolized by N-acetyltransferase.