Slow pathway (SP) ablation is an acceptable, standard method for atrioventricular nodal re-entrant tachycardia (AVNRT) ablation. The exact role of SP in the human heart and the possible negative implications of SP ablation are unknown. The current case report describes an unusual, brief, functional heart block, following radiofrequency ablation of the SP. Our findings highlight the peculiar property of the SP in maintaining conduction over an atrioventricular (AV) node, in circumstances of extreme autonomic imbalance. SP can be ablated without major conduction problems for AVNRT. Careful pre-ablation evaluation of the AV conduction pattern may assist in predicting occurrences of this type of heart block.