BACKGROUND Radiofrequency catheter ablation of concealed left-sided accessory pathways conventionally implies the introduction of several catheters for the assessment of electrophysiological properties as well as for the localization of the accessory pathways. METHODS Feasibility of radiofrequency ablation using a simplified two-catheter technique without coronary sinus catheterization was prospectively studied in 95 consecutive patients with a single concealed left free-wall accessory pathway. A 6F quadripolar catheter was introduced into the right atrium/right ventricle and tachycardia was induced by electrical stimulation. The presence of a concealed left-sided accessory pathway was suggested electrocardiographically (negative P wave in I and/or aVL during orthodromic tachycardia) or by earlier atrial activation in the pulmonary artery compared to the right atrium. Mapping of the mitral annulus and ablation were performed during orthodromic tachycardia or ventricular pacing using a 7F steerable catheter. Radiofrequency energy was applied at sites with the shortest VA interval. The procedure was considered effective if tachycardia could not be induced and if VA dissociation or exclusive nodal VA conduction were observed. RESULTS The procedure was initially successful in 93 out of 95 patients (98%). Mean number of applications were 3.2 +/- 2. Mean fluoroscopy time and total procedure duration were 14 +/- 9 and 108 +/- 33 minutes respectively. At a mean follow-up of 21 +/- 13 months, 2 patients required a second session because of tachycardia recurrence. CONCLUSIONS Radiofrequency catheter ablation of concealed left-sided accessory pathways can be safely, effectively and rapidly performed using a two-catheter technique without coronary sinus catheterization.