Abstract: A system and method is disclosed to improve the ability of physicians, researchers and others to digest large amounts of cardiac electrophysiologic data acquired during cardiac catheterization, improving their ability to visualize, interpret and act on its content. The technique addresses previous limitations imposed by the number of electrodes which can be simultaneously recorded and by difficulty in determining their locations in reference to intracardiac anatomy. It is based on the composition of multiple activation sequence mappings made in a single rhythm, effected by referencing the position of each of the catheter electrodes to a measurement grid which is stable with respect to the patient's heart. Using this approach, the number of endocardial sites which can be sampled in a stable rhythm is theoretically unlimited, resulting in realization of high resolution activation maps.