This study evaluated procedural considerations, risks, and long-term efficacy of radiofrequency modification of slow pathway conduction for treatment of atrioventricular node reentrant tachycardia in children < or = 10 years of age. Using a combined anatomic and electrographic mapping approach, modification of slow pathway conduction was achieved in 25 consecutive patients, although 4 had some form of transient atrioventricular block, indicating the need for caution in patient selection, catheter manipulation, and ablation.