Presents a method for determining the potentials over the surface of a three-dimensional volume due to internal current sources. The volume may be inhomogeneous and irregularly shaped. The method for determining the potentials uses N simultaneous equations which when solved produce the potentials at N different surface points. The N simultaneous equations are solved by an iterative technique on an IBM computer. A valuable application of this method is the determination of surface potentials from computer simulations of realistic electromotive distributions within the heart. In this connection, computer generated maps of surface potentials from a simulated heart have been produced and compare favorably with maps recorded from the torso of a dog.