The authors report a pseudoaneurysm in a 2-year-old boy presenting with fever, increasing cyanosis and right upper lung shadowing on a chest radiograph at six weeks following modified Blalock-Taussig shunt surgery. Echocardiography and a CT scan of the chest revealed a large pseudoaneurysm originating from the right subclavian artery at the proximal insertion of modified Blalock-Taussig shunt. The patient underwent aneurysmal resection, Blalock-Taussig shunt removal, right subclavian artery ligation and the creation of a central shunt between the ascending aorta and main pulmonary artery. Unfortunately, the patient died 3 hours after the operation.