Surface electrocardiographic changes after radiofrequency (RF) catheter ablation (RFCA) were observed in patients with idiopathic left ventricular tachycardia (ILVT), and the possible mechanisms were analysed. In 41 cases with ILVT who underwent the RFCA, the surface electrocardiograms (ECGs) before and after RFCA were recorded and the serum cardiac troponin I (cTnI) were measured before, immediately after, 4 h after and 24 h after RFCA. Seven patients developed different models and degrees of fascicular block after successful RFCA. The configurations of fascicular block had no dynamic alteration during the follow-up periods. No significant difference in the duration of the RF energy delivered, the numbers of RF lesion and the serum levels of cTnI between the patients with or without the electrocardiographic alteration was observed. Thus, the RFCA can cause the fascicular block in some of the patients with ILVT. The different distribution models of the left bundle branch, but not the damage degree to the endocardium induced by RF current, is the primary factor to the changes of ECG.