Effective electrical size (ratio of ventricular size to electrical activation wavelength) plays a significant role in governing reentrant arrhythmia dynamics. Due to similarities in effective size with the human, the rabbit has been suggested as the most useful experimental model for clinical investigations of fibrillatory arrhythmias. However, how well the effective size of the rabbit, or other small mammalians, correlates to the human during slower pacing rates (such as those often seen during anatomical scar-related reentrant arrhythmias), and importantly how it varies with frequency, is currently not well understood. We used computational ionic ventricular cell models of human, rabbit, rat and guinea pig to investigate interspecies differences in action potential duration, conduction velocity and activation wavelength restitution, and how these combine together to induce important rate-dependant variations in effective size. We conclude that the rabbit model has a closer effective electrical size to the human across a range of activation rates, although differences in effective size dynamics are seen at high frequencies. This suggests potentially important differences in the initiation and anchoring of reentrant waves around anatomical structures, highlighting the need for further investigation of the utility of such models for informing clinical scar-related arrhythmia knowledge.