In this paper, a method that uses magnetic extreme signals for equivalent source reconstruction is presented. Through simulation of specific current dipoles given as the sources of magnetic field signals, the feasibility of a multi-chamber heart model is investigated and the accuracy analysis of equivalent source reconstruction in inhomogeneous media is conducted. The magnitude of the magnetic extreme signals is indicative of the influence of volume conductor on the cardiac magnetic field is analyzed. The method is compared with other four methods which are the method of magnetic gradient extreme signals, the Nelder-Mead algorithm, the trust region reflective algorithm, and the particle swarm optimization algorithm against the criteria in terms of accuracy of source reconstruction and computation time of the algorithm. Results show that the method is practically useful for solving inverse cardiac magnetic field problems.