BACKGROUND: We aimed to share our experience of intra-atrial reentrant tachycardia mapping and ablation with a new grid-style multielectrode high-density mapping catheter (Advisor™ HD Grid) in pediatric and young adult patients with operated congenital heart disease. METHODS: All patients with operated congenital heart disease and intra-atrial reentrant tachycardia mapping with the new grid-style catheter between October 2019 and December 2022 were included (group 1), and the results were compared to those patients who operated with conventional catheter methods before this period (group 2). All procedures were performed using the EnSite Precision 3D mapping system (Abbott Laboratories, Abbott Park, Ill, USA) with a limited fluoroscopy approach. Data were evaluated retrospectively. RESULTS: In group 1 (n = 16; 9 male), the median age was 21 years (10-36), compared to 19 years (9-27) in group 2 (n = 10; 5 male). While irrigated radiofrequency ablation was pre-ferred in all patients, the median number of 15 lesions (8-38) in group 1 was significantly less than the median of 30 lesions (8-71) in group 2 (P =.027). The median procedure duration of 159 minutes (110-233) in group 1 was significantly shorter compared to 280 minutes (180-370) in group 2 (P <.05). Acute procedural success was achieved in all patients (16/16; 100%) in group 1 compared to 8/10 patients (80%) in group 2. During the median follow-up of 27 months (11-36), there was only 1 intra-atrial reentrant tachycardia recurrence in group 1 (1/16; 6.2%) and 2 recurrences (2/8; 25%) in group 2 during the median follow-up of 110 months (56-151). No complications related to the mapping catheter itself occurred. CONCLUSION: In the intra-atrial reentrant tachycardia ablation of children with congenital heart disease to increase procedural success and shorten the mapping duration, the utility of Advisor™ HD Grid mapping catheter seems to be a feasible alternative.