Catheter ablation with radiofrequency current has recently been introduced as a therapeutic regimen for symptomatic patients with the Wolff-Parkinson-White syndrome or atrioventricular (AV) tachycardia mediated by a retrogradely conducting (concealed) accessory AV pathway. These pathways may be located, although infrequently, in the anteroseptal region of the heart in close proximity to the AV node-His bundle conduction system. Any attempt to interrupt an anteroseptal accessory pathway therefore is subject to the potential complication of inadvertent impairment of normal AV conduction. This study was conducted to establish whether abolition of anteroseptal accessory pathways by radiofrequency current aimed at the atrial as opposed to the ventricular insertion of the pathway can be achieved with preservation of AV node-His bundle conduction. Twelve patients (mean age 37 +/- 13 years; 10 with Wolff-Parkinson-White syndrome, 2 with a concealed accessory pathway) were studied. In the majority of patients, radiofrequency current (500 kHz; mean energy 577 +/- 207 J) was applied through a steerable catheter with a long tip electrode placed in the anterior septal space at the atrial aspect of the tricuspid anulus, with the intention to destroy the atrial insertion of the accessory pathway. All pathways were successfully ablated. The AV node or His bundle conduction was not impaired in any patient. Right bundle branch block was induced in two patients (17%). There were no complications related to the procedure. It is concluded that catheter ablation from the right atrium using radiofrequency current provides effective and safe interruption of anteroseptal accessory pathways with good preservation of the normal conduction system.