The aim of this study was to investigate the differences between sustained and non-sustained forms of human atrial fibrillation (AF) using multielectrode endocardial recordings. Methods. Sixty-four pole basket catheters were deployed in the right atrium (RA) of 3 groups of patients: 1) patients with persistent AF (> 48 hours); 2) induced sustained AF (> 15 minutes); and 3) induced non-sustained AF (< 15 minutes). Beat to beat AF intervals (FF) were evaluated for each bipole. On the basis of signal characteristics and direction of wavefront propagation, the degree of spatial and temporal organization of AF was assessed. Results. Persistent AF showed the shortest FF intervals (161 ms) and lowest overall degree of AF organization, induced non-sustained AF the longest FF intervals (192 ms) and highest degree of organization. FF intervals of induced sustained AF were only slightly longer (169 ms) compared to persistent AF. Within each AF group, the lateral wall showed the highest degree of organization, the septal region the lowest. Conclusion. In humans, FF interval and overall degree of AF organization were found to increase significantly from sustained to non-sustained AF. Persistent and induced sustained AF, however, only slightly differed in these parameters.