I recently performed an ablation on a 67 y/o woman with AVNRT. She had inducible common variety (slow-fast) AVNRT on isoproterenol, and ablation was performed in the usual slow pathway location. Several burns were done, because no junctional rhythm was seen. Surprisingly, she had no inducible AVNRT on isoproterenol after the ablations, despite being easily inducible beforehand, and despite the fact that there was still 1:1 slow pathway conduction with atrial pacing! Retrograde conduction was also unaffected by the ablations. It appeared that the ablation had affected her tachycardia without modifying anterograde slow or retrograde fast pathway conduction. I wonder whether we ablated the upper common pathway linking the slow and fast pathways, whatever its nature. I won’t go into this long unresolved controversy on whether or not there is an UCP in AVNRT, whether it is atrial tissue, nodal tissue, or transitional cells. I do wonder whether anyone else has had a similar patient. I would propose that UCP ablation should be suspected when there is little or no junctional rhythm during burning, when there remains 1:1 slow pathway conduction during atrial pacing (stimulus to ventricular becomes longer than the atrial pacing cycle length without AV block), and when AVNRT is eliminated despite no evident effect on anterograde slow or retrograde fast pathway conduction. If anyone else has seen this, please share.