The purpose of this study was to compare the performance and clinical outcome of radiofrequency ablation of the substrate of atrioventricular (AV) nodal reentrant tachycardia (AVNRT) when guided by power output or temperature monitoring. Two sequential multicenter studies of power-controlled and open-loop, temperature-controlled radiofrequency ablation were analyzed in 171 patients undergoing AV node modification for the treatment of AVNRT. After successful ablation of AVNRT, complete elimination of slow AV node pathway function was accomplished more often with than without temperature monitoring (92% vs 69%, p = 0.005). Greater power was delivered to each patient with than without temperature monitoring (median 47 W, range 10 to 57, vs median 35 W, range 5 to 68, p = 0.001). Acute elimination of tachycardia (100% vs 96%), 3-month recurrence (6% vs 8%), procedural times (162 vs 170 minutes), fluoroscopy times (24.6 vs 29.5 minutes), complications (6% vs 3%), and catheter removals to check for coagulum (8% vs 6%) did not differ between patients treated with and without temperature monitoring, respectively. Power- and temperature-controlled radiofrequency techniques are highly successful with low complication rates for slow pathway ablation. Temperature monitoring may allow the safe delivery of more power, and the more complete elimination of slow AV node pathway function.