Background: The electrophysiological properties of atrioventricular nodal dual pathways have traditionally been investigated with premature stimuli delivered with right atrial pacing. However little is known about the functional characteristics of AV nodal inputs outside of this context. Methods: Superfused rabbit triangle of Koch preparations (n=8) and Langendorff-perfused hearts (n=10) were paced throughout the triangle of Koch, and mapped electrically and optically for: activation pattern, electrogram and optical action potential morphologies, stimulation thresholds, and stimulus-His (S-H) intervals. Optical mapping and changes in His electrogram morphology were used to confirm the activation pathway. Results: Pacing stimuli 2mm above the tricuspid valve (TV) caused fast pathway activation of the AV node and His with a threshold of 2.4±1.6mA. An area directly below the coronary sinus had high thresholds (8.6±1.4mA) that also resulted in fast pathway excitation (P<0.0001). S-H intervals (81±19ms) for fast pathway activation remained constant throughout the triangle of Koch, reflecting the AV delay. Stimuli applied <2mm from the TV resulted in slow pathway (SP) excitation or direct His excitation (4.4±2.2mA threshold, P<0.0001 compared to fast pathway). For SP/His pacing, S-H intervals showed a strong dependence on the distance from the His electrode, and were significantly lower than S-H intervals for fast pathway activation. SP/His pacing also displayed characteristic changes in His electrogram morphology. Conclusions: Optical maps and S-H intervals for SP/His activation suggest that AV conduction via SP bypasses the compact AV node via the lower nodal bundle, which may be utilized to achieve long term ventricular synchronization.