The invention relates to a system for providing an electrical cardiac activity map by means of electrical signals acquired by a plurality of surface electrodes on an outer surface of a living being (6). A cardiac structure position determination unit (12) determines a position of a cardiac structure, in particular, of the epicardial surface, based on provided projection images, wherein an anatomical cardiac model is adapted to the projection images. The projection images may be provided by an x-ray C-arm system (2). An electrical activity map determination unit (13) determines the electrical activity map at the cardiac structure based on the electrical signals, the positions of the plurality of surface electrodes also determined from the projection images, and the determined position of the cardiac structure. This allows determining the electrical activity map at the cardiac structure with high accuracy, without necessarily needing, for instance, an x-ray computed tomography system that would apply a relatively high x-ray radiation dose to the living being. The electrodes may be comprised in a vest (8).