Three-dimensional visualization of cardiac activation has become important for providing further insights into the pathophysiological mechanisms of arrhythmias and to increase the efficacy of catheter ablation. The noncontact mapping system enables a single-beat analysis of the reconstructed geometry of the cardiac chamber. In 8 patients with various kinds of arrhythmias (3 with atrial flutter, 2 with right ventricular outflow tract ventricular tachycardia, 1 with idiopathic left ventricular tachycardia, 1 with atrioventricular nodal reentrant tachycardia and 1 with concealed Wolff-Perkinson-White syndrome), non-contact mapping using an EnSite 3000 system was performed for the guidance of catheter ablation. The optimal sites for successful ablation were detected and all of these arrhythmias were successfully eliminated with the radiofrequency energy applications without any adverse effects. The computerized EnSite 3000 mapping system described here computes accurate isopotential maps that are a useful guide for catheter ablation.