Procainamide( proe-KANE-a-mide) (trade names Pronestyl®, Procan®, Procanbid®) is a pharmaceutical antiarrhythmic agent used for the medical treatment of cardiac arrhythmias, classified by the Vaughan Williams classification system as class Ia.

It blocks open sodium (Na⁺) 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 (EKG). This drug is used for both supraventricular and ventricular arrhythmias. For example, it can be used to convert new-onset atrial fibrillation, though it is suboptimal for this purpose.

Procainamide is administered intravenously or orally. When administered intravenously, a loading dose should first be given, though care should be taken not to cause hypotension. Procainamide's active metabolite is N-acetyl procainamide, which is excreted by the kidneys and the renal system.