Procainamide is a class 1a antiarrhythmic agent whose primary mechanism is related to its antagonism of cardiac sodium channels delaying phase 0 of the cardiac cycle. Procainamide and its metabolite N-acetyl procainamide also exert potassium efflux channel blocking effects prolonging the QT interval. Cardiac dysrhythmias range from bradycardia to torsades de pointes and ventricular fibrillation. In overdose, charcoal can be considered after securing the airway but the mainstay treatment for toxicity is treatment of underlying rhythms using sodium bicarbonate, magnesium, and overdrive pacing. In chronic toxicity, procainamide has been linked to a drug-induced systemic lupus erythematosus syndrome.