Junctional ectopic tachycardia is usually a limited but potentially life-threatening postoperative arrhythmia. We describe a case of malignant postoperative junctional ectopic tachycardia in a 13-month-old child who had undergone transatrial and transpulmonary repair of tetralogy of Fallot resistant to all conventional therapeutic measures and complicated by recurrent ventricular tachycardia. The arrhythmia was finally treated by open surgical cryoablation of the atrioventricular node and the implantation of a permanent pacemaker. The patient made an uneventful recovery followed by good long-term outcome.