Biological systems can inspire the development of biohybrid swimmers, which integrate abiotic and biotic components into an engineered construct embedding life-like biomimetic behaviours and functions. Demonstrations range from biohybrid rays and fishes based on sheets of optogenetic cardiomyocytes to neuromuscular-controlled swimmers. While these advancements hold promise, there are many areas of research that need to be advanced in parallel to enable applications of these devices, including the improvement of control strategies and biofabrication techniques, as well as the use of predictive computational modelling tools. In this study, we focus on the latter point, discussing a multiphysics computational model based on the Fluid-Structure-Electrophysiology Interaction (FSEI). Such state-of-the-art numerical tool allows us to conceive a new swimmer, referred to as BioBot, powered by cardiac muscle tissue. Its electrically-stimulated cyclic contractions thus provide the thrust for forward locomotion in the low to intermediate Reynolds number regime. The swimming performance of the BioBot are also investigated numerically with the aim of determining the optimal design. The robustness of the numerical results, make the proposed proof-of-concept a valuable resource to provide guidelines for improving the performance of future biohybrid and bioinspired systems, that can lead to novel advances in robotics, bioengineering and medicine.