Optical mapping of electrical activity from the surface of the heart is a powerful tool for studying complex arrhythmias. However, a limitation of traditional optical mapping is that the mapped region is restricted to the field of view of the sensor, which makes it difficult to track electrical waves as they drift in and out of view. To address this, we developed an optical system that panoramically maps epicardial electrical activity in three dimensions. The system was engineered to accomodate hearts comparable in size to human hearts. It is comprised of a surface scanner that measures epicardial geometry and a panoramic fluorescence imaging system that records electrical activity. Custom software texture maps the electrical data onto a reconstructed epicardial surface. The result is a high resolution, spatially contiguous, mapping dataset. In addition, the three-dimensional positions of the recording sites are known, making it possible to accurately measure parameters that require geometric information, such as propagation velocity. In this paper, we describe the system and demonstrate it by mapping a swine heart.