An optimal electrophysiologic mapping system for map- directed arrhythmia surgery should allow rapid and accurate interpretation of cardiac activation sequences. It should display activation or potential distribution data on an anatomically accurate 3-D model of the heart and allow fast, interactive control of viewing characteristics, such as rotation and which cardiac surfaces to display. The system described here employs two programs, GETP1C3 and MAP3, and runs on a Silicon Graphics, Inc. 4D/320GTX. It uses 3-D models of epicardial (epi) and endocardial (endo) surfaces created with the GETPIC3 program from a sequence of 2- D images of a heart. The individual surfaces are triangulated and may be smoothed using a spline function. MAP3 displays activation times either as static isochronous maps or as dynamic time-since-last-activation maps. In the case of dynamic activation maps, surface color denotes the time since that area activated. Potential distribution data may also be displayed dynamically. The program uses a mouse to control the real-time rotation of the model, and any surface (endo or epi) can be hidden interactively for better viewing of the data.