Rapidly replacing conventional thermal ablation techniques, pulsed field ablation (PFA) presents a non-thermal alternative offering improved safety and efficacy. The technique leverages irreversible electroporation to target myocardial cells, blocking the arrhythmogenic conduction. Achieving durable transmural lesions is a key to successful treatment and prevention of arrhythmia recurrence. However, reliable intraprocedural markers of such lesion formation are currently not available. Unipolar intracardiac electrograms (iEGMs) have been proposed as a potential tool to guide ablation. Our study aimed to develop a numerical model that allows exploration of the influence of PFA lesions of different sizes on unipolar iEGMs. The model was constructed around a three-dimensional rectangular geometry representing a cardiac tissue slab, on top of which an array of point electrodes was placed. Electrical signal propagation was modeled by coupling the bidomain equations with the Luo–Rudy cardiomyocyte model, accounting for anisotropic intracellular and extracellular conductivities. PFA lesion formation was simulated by introducing an additional current representing increased membrane permeability due to electroporation. The effects of lesion size on unipolar iEGMs were assessed by extracting extracellular potential values at the electrode array. The model was able to reproduce key electrophysiological features associated with lesion formation, including ST-segment elevation and a reduction in R-S amplitude. Furthermore, transmural lesions were associated with a marked reduction in negative deflection, decreasing the R–S amplitude to 0.15 mV, along with an increased injury current that reached a value of 9.3 mV. Although limited to steady-state lesion formation without considering recovery dynamics, the model provides insights into iEGM behavior following ablation and offers rationale and guidance for future experimental validation.