BACKGROUND: Idiopathic ventricular arrhythmias (VAs) arising from the left anterior fascicle (LAF) are uncommonly seen, and their characteristics still need to be sufficiently investigated. This study aimed to conclude these VAs' characteristics and explore efficient ablation strategies. METHODS: Data were analyzed from 118 patients undergoing successful catheter ablation for LAF VAs. Patients were divided into three groups based on target sites in LAF: proximal-LAF group (n = 30, from the common trunk of the left bundle branch to the LAF below the right coronary cusp (RCC), middle-LAF group (n = 35, the LAF below the RCC and left coronary cusp (LCC), distal-LAF group (n = 53, the LAF below LCC to the LAF terminal). RESULTS: From proximal- to distal-LAF, VAs showed a gradually decreased Purkinje-ventricular (PV) and His-ventricular (HV) interval. For proximal-LAF VAs, a distance from the sites recorded with the earliest Purkinje potential to RCC of 4.08 ± 1.03 mm predicted successful ablation in RCC. There are significant differences among the three groups in QRS duration, R/S ratio in V6, and Lead I. Using these three ECG characteristics as a panel to predict the origin of LAF VAs, the area under curve (AUC) was 0.96% and 95% confidence interval (CI) was 0.916-1.0 in the proximal- and middle-LAF group, the AUC was 0.998 and 95% CI was 0.994-1.0 in the middle- and distal-LAF group. CONCLUSION: When LAF is anatomically divided into proximal, middle, and distal segments, QRS duration and R/S ratio in Leads V6 and I are available to predict the origin and promote a successful catheter ablation. In addition, combining these three ECG characteristics as a panel can better facilitate the prediction of LAF-VA origin.