Atrial fibrillation (AF) is a public health burden with increasing incidence. Reentry events are drivers of AF, and investigation of their underlying mechanisms is ongoing. The influence of the conduction velocity (CV) on reentry events has been thoroughly studied in contrast to CV restitution. We simulated electrical wave propagation with the diffusion reaction eikonal alternant model (DREAM) in tissue slabs. Scenarios with combinations of three maximal longitudinal CV (CV0) values (200, 400, and 600 mm/s) and 12 CV restitution curve morphologies extracted from electrode measurements in 13 patients with persistent AF, resulting in 36 experiments, were considered. In each experiment, an S1-S2 protocol was applied to induce reentry. The vulnerable window and average duration of reentries of each experiment were compared based on the steepness of the CV restitution. The vulnerable window increased with decreasing steepness of the CV restitution curve. The maximum increase was 59.6, 40.8, and 22.8 % for the three CV values, respectively. Similarly, for the average duration of reentries, a maximum increase of 38.6, 72.5 and 22.8 % was observed for less steep CV restitution. In conclusion, shallow CV restitution curves are characteristic of more vulnerable tissue and can contribute to maintenance of longer AF episodes.