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Introduction: Reports suggest that coronary sinus (CS) or left atrial ablations may be necessary for treatment of AV nodal reentrant tachycardia (AVNRT) with earliest retrograde atrial activation in the CS. We assessed the efficacy of standard right atrial catheter ablation approaches in these tachycardias and determined the incidence of earliest activation in the CS in AVNRT., Methods and Results: We retrospectively evaluated intracardiac recordings from 225 consecutive patients who underwent electrophysiologic studies and radiofrequency (RF) ablation for AVNRT in two institutions. Atrial activation during AVNRT was evaluated using multiple catheters according to standard protocol used in our laboratories. RF ablations in the triangle of Koch were performed in all patients. Eighteen of 225 patients (8%) had earliest activation in one of the CS poles. The demographics and AVNRT characteristics of these 18 patients were similar to those of the other 207 patients who did not have CS as earliest activation site and included both typical and atypical AVNRT. Following RF ablation, none of the 18 patients had inducible AVNRT., Conclusion: Successful RF ablation can be performed at standard sites in the triangle of Koch regardless of earliest site of atrial activation. The incidence of CS as earliest retrograde atrial activation site in AVNRT is 8%.