Various embodiments are described herein for a system, method, and device for identifying focal source locations of electrophysiological activity in an organ. The system, method and device may also be used to guide catheter ablation of the organ. An electro-gram signal can be obtained from a location in the organ, and it can be determined if the electrogram is periodic and, if so, the corresponding periodicity cycle length. A plurality of peaks associated with the cycle length can be identified. The location can be identified as a focal source location when the periodicity cycle length and the plurality of peaks have focal source characteristics. Methods are also described for identifying a direction of wave propagation and identifying multiple periodicities within an electrogram signal.
