Background: Pulsed Field Ablation (PFA) is a novel energy modality for treatment of cardiac arrhythmias. The impact of device-tissue contact on lesion formation by PFA has not been conclusively assessed. Objective: To evaluate the effects of tissue proximity on cardiac lesion formation with a biphasic, bipolar PFA system. Methods:PFAwasdeliveredon theventricularepicardial surface in a porcine heart model via a 4-electrode catheter (n5 8). An offset tool was used that placed the deliveries 0 mm, 2 mm, and 4 mm away from the tissue and surrounded with heparinized blood. Lesions were assessed using tetrazolium chloride (TTC) staining. Numerical models for both the experimental setup and the continuous blood-field model (setup without offset tool) were created. Results: Lesion dimensions decreased as the offset between epicardial surface and electrodes increased. Lesion depth averaged4.360.4mm,2.760.4mmand1.360.4mmfor the0, 2, and 4-mmoffset distances, respectively. Lesion width averaged 9.4 6 1.1 mm, 7.56 0.8 mm and 5.86 1.4 mm for the 0, 2, and 4-mm offset distances respectively. Numerical modeling demonstrated lesion creation with and without offset tool. Conclusion: Using a bipolar, biphasic PFA system resulted in cardiac lesions even in the absence of direct tissue contact of the ablation electrodes. Further, the relationship between lesion depth and offset distance was linear, and the deepest lesions were created with direct electrode contact. Therefore, close electrode tissue proximity increases the likelihood of achieving transmural lesions via maximizing the electric field penetration into the target tissue.