As children with cardiac malformations grow older, it appears that although their hemodynamic abnormalities may have been corrected by surgery, an increasing number of these patients have severe and possibly lethal arrhythmias. Atrial surgery and Fontan-type operations are complicated by atrial tachyarrhythmias that are difficult to predict and control. The relation between sudden death and ventricular tachycardias in patients who have undergone tetralogy of Fallot repair is still controversial. Application of radiofrequency energy now offers an alternative to pharmacologic therapy and surgery for children who have symptomatic tachyarrhythmias and need life-long therapy. Initial results are encouraging, with a very low morbidity, especially for children who have supraventricular reentrant tachycardias due to accessory pathways. However, the place of ablation in children is not yet fully delineated, as long-term follow-up evaluations are still lacking at this time. For this reason, antiarrhythmic agents, including class Ic drugs and amiodarone, should be tried first, especially in very young children. Indications for antiarrhythmic surgery are becoming very rare, due to the introduction of ablation techniques. For children who have life-threatening ventricular arrhythmias, implantation of a cardioverter-defibrillator represents a new therapeutic option, one that may also be used as a bridge to heart transplantation.