Introduction: Pulsed electric field (PEF) ablation relies on the intersection of a critical voltage gradient with tissue to cause cell death. Field-based lesion formation with PEF technologies may still depend on catheter-tissue contact (CTC). The purpose of this study was to assess the impact of CTC on PEF lesion formation with an investigational large area focal (LAF) catheter in a preclinical model. Methods: PEF ablation via a 10-spline LAF catheter was used to create discrete RV lesions and atrial lesion sets in 10 swine (8 acute, 2 chronic). Local impedance (LI) was used to assess CTC. Lesions were assigned to 3 cohorts using LI above baseline: No Tissue Contact (NTC: ≤∆10Ω, close proximity to tissue), Low Tissue Contact (LTC: ∆11-29Ω), and High Tissue Contact (HTC: ≥∆30Ω). Acute animals were infused with triphenyl tetrazolium chloride (TTC) and sacrificed ≥2hrs post-treatment. Chronic animals were remapped 30 days post-index procedure and stained with infused TTC. Results: Mean (±SD) RV treatment sizes between LTC (n=14) and HTC (n=17) lesions were not significantly different (depth: 5.65±1.96mm vs 5.68±2.05mm, p=0.999; width: 15.68±5.22mm vs 16.98±4.45mm, p=0.737) while mean treatment size for NTC lesions (n=6) was significantly smaller (1.67±1.16mm depth, 5.97±4.48mm width, p<0.05). For atrial lesion sets, acute and chronic conduction block were achieved with both LTC (N=7) and HTC (N=6), and NTC resulted in gaps. Conclusions: PEF ablation with a specialized LAF catheter in a swine model is dependent on CTC. LI as an indicator of CTC may aid in the creation of consistent transmural lesions in PEF ablation.