Background : The present study was designed to investigate the relation of the anatomic features of the triangle of Koch and the reentrant circuit of AVNRT. Methods: We measured the angiographic distance between coronary sinus ostium and His (CS Os-His distance) based on the electrode location in CS and His which was taken from RAO 30째view during the RF ablation procedure for AVNRT. The study subjects were 21 patients (Male 8, Age 51.1짹14.6). We evaluated the correlation between the CS Os-His distance and the following variables; the maximum atrio-His interval on His electrogram., the AVNRT cycle length, atrio-His(AH) and HA���interval during AVNRT, location of the success RF application sites. We also compared the CS Os-His distance between the slow pathway ablated and modified patients. Results: The mean Cs Os-His distance was 11.7짹4.2mm(5.3 mm-18.0 mm). There were no significant correlations between AVNRT cycle length, AH interval during AVNRT, HA���interval during AVNRT, Max. AH interval and CS Os-His distance. The CS Os-His distance of the slow pathway modified patients and that of ablated patients were not different(12.1짹4.2 mm vs 10.9짹4.3 mm, p=0.076). The patients whose success site were midseptal area showed a tendency having longer Cs Os- His distance than those with success site on posteroseptal area(13.5짹3.3 mm vs 10.1짹4.4 mm, p=0.056). Conclusion; The electrophysiologic features of reentrant circuit of AVNRT do not seem to be determined by the size of triangle of Koch.