By applying this electrophysiologic principle of differential tissue capture to help identify the location of the compact AV node, which is in close proximity to the His bundle. Ventricular pacing was performed initially at high output to capture both the basal right ventricular myocardium and the His bundle and the output was gradually lowered to lose His bundle capture. The QRS duration is relatively narrow with high output pacing and increases when the pacing output is lowered, representing ventricular myocardial capture alone. Finally, loss of ventricular capture is seen with further reduction of pacing output. This maneuver has been shown to aid in determining the proximity of the ablation catheter to compact AV node as was validated by successful ablation at this site. Parahisian pacing in conjunction with av nodal ablation has recently been described in the literature.