Aims The implantable loop recorder (ILR) continuously monitors the heart’s electric activity by means of a subcutaneous bipolar electrogram (Elg). Currently, the relationship between the Elg and the surface electrocardiogram (ECG) has been poorly documented. This model-based study aimed at investigating the differences between the bipolar surface and subcutaneous signals, as well as the effect of the insulating boundary of the ILR on these signals. Additionally, the model is used for determining the optimal implant location of the device. Methods and results Sinus rhythm ECG of a complete heart cycle was simulated by means of a biophysical model. Different volume conductors were created to investigate the effect of the insulating boundary of the ILR. The Elg closely matched the nearby bipolar ECG, both in morphology and in amplitude. The optimal localization and orientation of the ILR was found to depend on the Elg signal feature of interest, e.g. PQ, QRS, or STT waveforms. Conclusion The differences between the bipolar ECG on the surface and the subcutaneous electrogram are negligible. The optimal implant location may be based on nearby surface recordings. The simulation model is an eligible tool for determining the optimal implant location for the ILR, for all signal features of interest.