The aim of our study was to evaluate the hemodynamic effects and clinical outcomes of transcatheter fenestration in patients who developed Fontan failure.Between January 2014 and December 2022, among a total of 187 patients undergoing the Fontan operation, 10 (6 males, 4 females; median age: 10.9 years; range, 4.2 to 23 years) who underwent transcatheter creation or dilation of a Fontan fenestration due to the development of Fontan failure were retrospectively analyzed. Demographic data, laboratory results, echocardiographic findings, and catheterization parameters of the patients were recorded. The patients were classified into two groups based on the timing of Fontan failure: those who underwent fenestration before hospital discharge constituted the early-stage group, while those who underwent fenestration after discharge were assigned to the late-stage group. These two groups were compared in terms of hemodynamic parameters, changes in oxygen saturation, and complication rates.Transcatheter fenestration was performed in five patients due to Fontan failure in the early postoperative period, and in five patients in the late period. The median follow-up duration was 2.2 (range, 0.1 to 6) years. Following the procedure, pleural effusion regressed in four patients; median systemic venous pressure decreased by 3.4 (range, 2 to 9) mmHg, while median oxygen saturation dropped by 5.9% (range, 3 to 9%). Clinical improvement was observed in 70% of the patients within the first month. However, one patient died on postoperative Day 44 due to low cardiac output. Fenestration was performed in three patients with protein-losing enteropathy, and clinical improvement was achieved in all of them.Transcatheter Fontan fenestration is a reliable therapeutic option for reducing systemic venous pressure and achieving hemodynamic improvement in symptomatic Fontan patients. Our study highlights the low complication rates and the potential of this procedure to yield favorable clinical outcomes. Transcatheter fenestration plays an important role in the management of high-risk Fontan patients.