Radiofrequency (RF) catheter ablation is now a widely used technique for treating cardiac arrhythmias—it is considered as routine first line treatment for most arrhythmias. Although its effectiveness is very high it has a low but definite risk of complications.1 ,2 Complete atrioventricular (AV) block is one of the more common complications. Its importance is raised as many patients with this arrhythmia are young and, should they have AV block, they would need permanent cardiac pacing for a long expected lifetime. AV block may be caused by the delivery of RF energy in the septal region, close to the compact AV node or proximal His bundle in patients with mid or anteroseptal accessory pathways, or in patients with atrioventricular nodal reentrant tachycardia (AVNRT). Septal localisation of the accessory pathways is quite rare and the risk of AV block is balanced by the potential risk of life threatening arrhythmias that patients with Wolff-Parkinson-White syndrome may have. In contrast, it is a major risk for patients with AVNRT considering the benign nature and relatively high incidence of this arrhythmia in the general population.