Atrial fibrillation is a common arrhythmia, which is frequently difficult to control. Symptoms and ventricular dysfunction may be caused by a rapid ventricular response to atrial fibrillation. Radiofrequency catheter ablation techniques for ventricular rate control have been developed, including AV node modification and AV node ablation with pacemaker implantation. For both AV node modification and ablation, radiofrequency energy is applied via a 4-mm tipped electrode catheter. For AV node ablation radiofrequency energy is applied near the compact AV node or His bundle via the right atrium, or occasionally at the His bundle via the left ventricle. For AV node modification radiofrequency energy is applied in the low middle or posterior septal right atrium near the tricuspid valve annulus. Both techniques can effectively control ventricular response to atrial fibrillation and the associated symptoms, although AV node modification is effective in only about 70% of patients compared to AV node ablation, which is effective in nearly 100%. In patients responding to AV node modification, maximal and mean ventricular response to atrial fibrillation is reduced by 25% to 35% chronically. Inadvertent AV block may occur during attempted AV node modification. It seems appropriate to attempt AV node modification prior to AV node ablation in patients with refractory atrial fibrillation and rapid ventricular response, in order to avoid the need for permanent pacemaker implantation. Although unproven, studies suggest that the mechanism by which AV node modification achieves ventricular rate control may be slow-pathway ablation in the low posterior septal right atrium.