BACKGROUND Template matching, a technique that examines the similarity between two QRS complexes, has not been broadly applied clinically. METHODS The 16 patients enrolled in this study underwent radiofrequency catheter ablation (RFCA) at the site of five ventricular tachycardias (VT) and of premature ventricular contractions (PVC) arising from 25 sites in the right ventricular outflow tract (RVOT), under the guidance of conventional pace and activation mapping. After RFCA, (a) a template-matching score using a correlation coefficient, and (b) a pace-map score were calculated at 30 successful and 48 unsuccessful ablation sites. RESULTS The template-matching score at successful ablation sites (94 +/- 4%) was significantly higher than at unsuccessful (85 +/- 9%) ablation sites (P < 0.001). A > or = 90% average matching score identified successful ablation sites with a sensitivity of 90% and specificity of 69%. While there was a significant correlation between the template-matching score and visually judged pace-map score (r = 0.63, P < 0.0001), the area under the receiver operating characteristic curve of the template matching score was larger than that of the pace-map score (0.80 vs. 0.67). CONCLUSIONS Automated template matching was useful for localizing the optimal ablation site during RFCA of RVOT-VT/PVC.