Case-report: A 71-year-old female had slow-fast atrioventricular (AV) nodal reentrant tachycardia (AVNRT) and prolonged PR interval (260 ms) during sinus rhythm. Diagnosis was verified during electrophysiological study. At the beginning of the procedure AH- and HV-intervals were 174 ms and 48 ms respectively. Ablation targeting site was determined at the superior edge of the CS ostium guided by bipolar and unipolar recording. Slow pathway potential characterized by atrial component of the bipolar EG had qRs-like morphology, and the AV ratio was 1.0. The unipolar targeting potential showed dual-component atrial EG, where the first component was a positive delta-like wave, which corresponded to isoelectric phase preceding qRsr’-like configuration on a bipolar EG. The second rS/RS component of unipolar EG had a sharp and biphasic morphology and corresponded to so-called R wave on a bipolar atrial EG. RF-application at this site with target temperature of 55 C and power output 45 W resulted in appearance of accelerated junctional rhythm without VA conduction block. Following the elimination of the slow pathway, the PR and atrio-His intervals became shortened from 260 and 174 to 200 and 100 ms, respectively The slow pathway RF-modfication improved conduction of the proximal AV nodal structures and resulted in decreasing of the PR and atrio-His intervals. Moreover, the improvement of AV conduction after the slow pathway ablation lasted for at least 18 months. Conclusion: Main clinical implication of unipolar and bipolar recording for the AV slow pathway mapping and ablation in patients with prolonged PR concludes that it approach can allow treating AVNRT avoiding AV conduction impairmen