Atrio-ventricular node reentry tachycardia (AVNRT) is the most common paroxysmal tachyarrhythmia in adolescents and young adults.An injury to the atrio-ventricular node is a known complication associated with catheter ablation.Late occurrence ofatrio-ventricular block is unusual.We investigated atrio-ventricular node conduction with exercise stress testing and ambulatory Holter monitoring at least one year after radiofrequency ablation of the slow pathway performed before patients 18th birthday: