The aim of this study was to compare the efficacy of transaortic (n = 54) and transseptal (n = 28) techniques during radiofrequency (RF) ablation of left accessory pathways (n = 75) in both left posteroseptal and free-wall locations in 73 consecutive patients (mean age 32 +/- 15 years). The transseptal approach included transseptal puncture and use of a retained long sheath in the left atrium (n = 24) or direct insertion of the mapping/ablation catheter via a patent foramen ovale (n = 4). Transseptal RF ablation was used as the primary method in 23 patients or at a separate session after the transaortic RF ablation failed in 5 patients. Transaortic RF ablation was used as primary method in 50 patients and after failed transseptal ablation in 4 patients. Transaortic ablation was successful in 47 (87%) of 54 procedures, transseptal ablation in 24 (86%) of 28 procedures, with total RF ablation success in 70 (96%) of 73 patients. The transseptal puncture/long sheath method was successful in 23 (96%) of 24 patients. This latter technique resulted in more stable positioning and easier manipulation of the ablation catheter. Switching from transseptal puncture/long sheath to transaortic technique was needed in 1 of 24 patients, from transseptal/patent foramen ovale approach to the transaortic route in 3 of 4 patients, and from the transaortic to the transseptal approach at a separate session in 5 patients. The age of patients and number of RF lesions were similar in the two groups. Fluoroscopy time was lower for the transseptal group (81 +/- 57 vs 121 +/- 81 min; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)