In synchronized cardioversion, an electric current is delivered to the heart to correct an arrhythmia. This procedure may be done electively in a stable patient with recurrent atrial fibrillation or urgently in an unstable patient with such arrhythmias as paroxysmal supraventricular tachycardia, atrial flutter, atrial fibrillation, and VT with a pulse.

Compared with defibrillation, synchronized cardioversion uses much lower energy levels and is synchronized to deliver an electric charge to the myocardium on the peak R wave.

The procedure causes immediate depolarization, interrupting reentry circuits (abnormal impulse convduction that occurs when cardiac tissue is activated two or more times, causing reentry arrhythmias) and allowing the SA node to resume control.

Synchronizing the electric charge with the R wave ensures that the current won't be delivered on the vulnerable T wave and disrupt repolarization. This reduces the risk that the current will strike during the relative refractory period of a cardiac cycle and induce VF.