Methods and systems for computing epicardial surface electric potentials based on measured body surface electric potentials, where the methods and systems include representing at least one geometric relationship between at least one body surface electric potential measuring system and the epicardial surface as a multidimensional matrix, estimating an inverse of the multidimensional matrix based on a Generalized Minimum Residual (GMRes) method, and, based on the inverse matrix and the measured body surface potentials, determining the epicardial surface electric potentials.