Cardiac arrhythmias affect millions of people worldwide. The complex electrophysiological mechanisms underlying these arrhythmias require comprehensive investigation to improve diagnosis, treatment, and prevention. Epicardial electrical mapping is a valuable tool for characterizing the propagation of electrical activity across the heart’s surface. This study aims to develop and validate a custom epicardial electrical mapping system using a microelectrode array (MEA). The study used 18 New Zealand white rabbits as the animal model. A series of custom designed MEAs were developed, with iterative improvements to the mechanical, electrical, and optical characteristics. The MEAs were constructed using polyethylene terephthalate (PET) sheets as the structural material, with different electrode configurations. Optical characterization demonstrated the effectiveness of PET as a substrate material for MEAs in concurrent optical mapping applications. The analysis revealed that PET exhibits high light transmittance, reaching up to 87% at wavelengths relevant to the optical mapping process. The developed epicardial electrical mapping system was able to capture the electrical activity in the isolated rabbit heart model. The flexible polyimide film used in the final MEA design allowed for better conformity to the heart’s surface to acquire signals.