Atrial fibrillation is an electrical disorder of the upper chambers of the heart (atria) in which they are activated in an irregular haphazard fashion at a very high rate so that they fail to contract. Usually atrial fibrillation does not cause ventricular fibrillation as most of the atrial signals in atrial fibrillation are prevented from reaching the ventricle by the atrioventricular node. But when there is an atrioventricular bypass tract (an accessory pathway), the fast atrial signals can reach the ventricle and activate it at a very high rate. Such high rates of activation prevents the ventricle from contracting in an organized fashion and can lead on to ventricular fibrillation. This occurs in a condition called WPW syndrome with atrial fibrillation, which is potentially life threatening and is ideally treated by immediate direct current shock for termination of the abnormal rhythm and restoration of normal sinus rhythm. This should be followed by medications or radiofrequency catheter ablation (a form of electrical treatment using radiofrequency current applied through small electrodes at specific locations in the heart) to prevent recurrence of the situation.