Background: Ventricular arrhythmias (VAs) may arise from the aortic sinuses and have electrocardiographic and electrophysiological characteristics that suggest a left (LCC) or right coronary cusp (RCC) origin. However, VAs that arise near the junction of those two cusps (L-RCC) may have unusual features. Objectives: The purpose of this study was to examine the electrocardiographic and electrophysiological characteristics of VAs arising from the L-RCC. Methods: We studied 155 patients with idiopathic VAs with either left or right bundle branch block and an inferior QRS axis morphology and five control subjects undergoing a pacing study. Results: For 146 of the 155 patients, the origin determined by the successful ablation site was at the L-RCC in five, LCC in 13, RCC in six, non-coronary cusp in two, right ventricular outflow tract in 108, left ventricular outflow tract in five, left ventricular epicardium in four, and pulmonary artery in three. A qrS pattern in leads V1-V3 was observed only in the VAs with an L-RCC origin. The propagation map revealed that the direction of the propagating wave front from the L-RCC origin produced a vector compatible with a q wave and that the anterior activation to the right ventricular outflow tract via the LCC or RCC formed the r wave. Pacing performed at multiple sites in the aortic root in the control subjects demonstrated that only pacing from the L-RCC could reproduce a qrS pattern in leads V1-V3. Conclusions: This study revealed that a qrS pattern in leads V1-V3 suggests a site of origin at the L-RCC. © 2008 Heart Rhythm Society.