Abstract Appropriate targets for catheter ablation of atrial fibrillation (AFib) beyond pulmonary vein isolation (PVI) are still controversially discussed. Since available parameters to analyze the vulnerable substrate are very limited, there is the need to define and understand tailored features. Mapping during AFib can be particularly challenging due to its non-repetitive nature. Amongst others, temporal stability despite changing activation sequences is an essential requirement for features applied to AFib maps. The local cycle length (CL) and duty cycle (DC) offer novel measures to characterize the atrial substrate during AFib. This study aims at providing first insights into the temporal stability of CL and DC during AFib in order to assess the suitability of both features for the characterization of the individual substrate and tailor ablation strategies in future. In patients with recurrent AFib after PVI, two high-resolution 3D electro-anatomical maps were recorded sequentially during AFib before any ablation. Intracardiac electrograms (EGMs) were preprocessed to improve local signal quality and far field suppression. EGMs were recorded with a multipolar, basket-shaped high-density mapping catheter. Local CL and DC distribution were visualized using scatter plots and histograms. CL quantifies the time between subsequent local activations, DC quantifies the fraction of CL with local EGM activity, and the confidence (conf) feature quantifies the spatiotemporal consistency of EGM morphology. Only recordings with conf > 0.6 are analyzed. Feature calculation is based on a weighted conglomerate of all acquisitions within a series of beats. Adjustable CL and DC thresholds allow highlighting regions within the 3D map for individual spatial analysis. Both the global distributions and the local occurrence of CL and DC were compared in order to assess temporal stability. Four patients (2x paroxysmal AFib, 2x persistent AFib) were enrolled. All subjects underwent repeat ablation after PVI due to recurrence of AFib. Table 1 summarizes mapping parameters for both AFib maps in individual patients. Despite differences in mapping time and the number of EGMs, CL and DC histograms were significantly similar when comparing maps within one patient. For individually selected ranges of CL and DC in the upper left corner of the scatter plot (short CL and high DC), localization of corresponding areas was comparable in both 3D maps. An example is shown for patient I in the left and central column of the figure. CL and DC distributions were temporally stable features for all patients in this study cohort. Localization of EGMs of given CL and DC range within the 3D maps were comparable but not identical for arbitrarily selected ranges. CL and DC can therefore be considered valid features for substrate characterization during AFib. Further studies will need to investigate how ablation strategies can be derived from individual CL and DC distributions.