BACKGROUNDNo evidence exists regarding whether Tissue Proximity Indication (TPI), an impedance-based contact indicator, can improve in vivo lesion formation and durability during pulsed field ablation (PFA). OBJECTIVEThis in vivo study investigated the relationship between catheter-tissue contact and lesion formation. METHODSIn 5 porcine subjects, PFA applications were delivered at 35 atrial target sites using the VARIPULSE™ variable-loop circular catheter with the CARTO 3™ mapping system. We compared acute ablative low voltage zones (LVZ <0.5 mV), chronic LVZ, and pathological lesions between no/minimum contact (TPI-negative/flickering TPI-positive status) and consistent tissue contact (consistent TPI-positive status) for typical clinical scenarios, and tissue tenting (TPI-positive status with electrodes extensively away from the 3D mapping surface) for safety margin. Ultrasound imaging also confirmed contact category assessments. RESULTSAcute and chronic LVZs were significantly larger with consistent contact compared with no/minimum contact, including pathological lesion length (36.0±12.5 mm vs 17.4±15.2 mm; P=0.002) and maximum width (10.3±2.7 mm vs 5.7±5.1 mm; P=0.035), results with tenting (length: 34.6±11.7; width: 11.3±1.9 mm) were comparable to consistent contact. Lesion transmurality was achieved in all lesions with consistent contact or tissue tenting, but only in 54.5% with no/minimum contact (P=0.001 for each). The TPI-based electrode contact distance, measured as the cumulative length of the multi-electrode catheter tip positive for TPI, significantly correlated with lesion length, maximum width, and transmurality. CONCLUSIONConsistent TPI-based contact during PFA was strongly associated with distinct chronic transmural lesions, emphasizing the importance of tissue contact in optimizing circumferential lesion formation with circular PFA catheters.