Background The detailed electrophysiological characteristics of atrial fibrillation (AF) initiating non-pulmonary vein (PV) triggers excluding origins from the superior vena cava (SVC) and left atrial posterior wall (LAPW) (Non-PV-SVC-LAPW triggers) remain unclear. This study aimed to clarify the detailed electrophysiological characteristics of non-PV-SVC-LAPW triggers. Methods Among 446 AF ablation procedures at 2 institutions, patients with reproducible AF initiating non-PV-SVC-LAPW triggers were retrospectively enrolled. The trigger origin was mapped using the self-reference mapping technique. The following electrophysiological parameters were evaluated: the voltage during sinus rhythm and at the onset of AF at the earliest activation site, coupling interval of the trigger between the prior sinus rhythm and AF trigger, and voltage change ratio defined as the trigger voltage at the onset of AF divided by the sinus voltage. Results Detailed electrophysiological data were obtained at 28 triggers in 21 patients. The median trigger voltage at the onset of AF was 0.16mV and median trigger coupling interval 182msec. Normal sinus voltages (≧0.5mV) were observed at 16 triggers and low voltages (<0.5mV) at 12 triggers. The voltage change ratio was significantly lower for the normal sinus voltage than low sinus voltage (0.20 vs. 0.60, p = 0.002). The trigger coupling intervals were comparable between the normal sinus voltage and low sinus voltage (170ms vs. 185ms, p = 0.353). Conclusions The trigger voltage at the onset of AF was low, regardless of whether the sinus voltage of the trigger was preserved or low.