Introduction:Balloon dilation and stenting of branch Pulmonary arteries (PA) is standard of care in post arterial switch operation (ASO) branch PA stenosis. We report a case of late onset Aorto-Pulmonary fistula following stenting for LPA stenosis in an 8-year-old male, which was diagnosed on operating table. Case Report: The patient had undergone neonatal arterial switch operation, but subsequently developed PA stenosis. He had undergone pulmonary valvotomy with trans annular patch and bilateral branch PA augmentation at 6 months of age. He underwent stent insertions to LPA and MPA at 3 years and 6 years of age, respectively. He developed severe PS and Moderate PR and was referred for Surgical Correction. A redo sternotomy was done, and cardiopulmonary bypass initiated. Attempts to dissect PA from Aorta was abandoned in view of dense adhesions. When we opened MPA, pulsatile bleeding was noted from a 5mm x 5 mm fistulous opening between posterior wall of MPA close to LPA origin and anterior wall of Aorta. Attempts to close the defect with pledgetted sutures failed due to present of stent remnants. An attempt to occlude the fistula temporarily with a Foley balloon also failed as the balloon got punctured by stent bits. We applied finger pressure to control bleeding and cooled patient down to 18 degree Celsius. Aorta was cross clamped, went on short circulatory arrest and an 8Fr Foley catheter was inserted through fistula to aortic root to deliver cardioplegia. Fistula was closed with a bovine pericardial patch using parachute technique. Confluence was augmented with homograft and RV to PA Homograft conduit was anastomosed to it. Patient had an uneventful recovery. Review of preoperative imaging and clinical data did not suggest any evidence of existence of fistula. Conclusion: Late onset Aorto – PA fistula can occur due to erosion of aortic and PA wall by LPA stent and may not be detected clinically. Surgical management can be challenging and may require circulatory arrest.