Background: We aim to determine the characteristics of the HB potentials in atrioventricular nodal reentrant tachycardia (AVNRT), and elucidate whether these can provide clues for identification of patients with slow pathway (SP). Methods：We studied the electrophysiological findings of 162 consecutive patients with symptomatic AVNRT due to slow-fast or fast-slow type reentry (n=112) and AV reentrant tachycardia (AVRT) (n=50). Maximal HB potential (taken as HBmax, which was highest in amplitude) among HB cloud was recorded for comparison. For AVNRT patients: (1)The AH interval (A2H2) at the “jump” during programmed atrial stimulation (taken as a reflection of slow-pathway conduction time); (2)The distance from HBmax to the successful SP ablation site (HBmax-ABL) and from HBmax to the ostium of coronary sinus (HBmax-CSO). Results: HBmax was 0.29±0.10mV in AVNRT patients, whereas it was 0.17±0.05 mV in AVRT group (p<0.0001). Likewise, the HBmax duration was 22±5 ms in the AVNRT group and 16±3 ms in the AVRT group(p<0.0001). The area under the ROC curve of HBmax amplitude in AVNRT patients was 0.86 and the optimal HBmax cut-off to predict AVNRT was≥0.22 mV with a sensitivity of 0.78 and specificity of 0.84. HBmax-CSO was positively correlated with HBmax-ABL, and HBmax-ABL was positively correlated with A2H2. Conclusions: HBmax amplitudes were higher and durations longer in patients with AVNRT, as compared to those with AVRT. Moreover, the distance between HBmax and successful ablation site was positively correlated with the SP conduction time and with the distance from HBmax to the CS ostium.