Cardioversion is an electrical shock that is synchronized so that only the atria are affected - not the ventricles- as in defibrillation. The hope is that once the atria are depolorized at the same time the SA node will reassert itself as the pacemaker.It does require moderate sedation, and is over quickly. The joules that are used are about 100. However the inderlying cause of the atrial fib has not changed it is not unusual for patients to reconvert to the atrial fib.