A method is provided for determining cellular electrical potentials using a state estimator. The state estimator is generated using at least an electrical source model and an electrical conduction model. One or more parameters or states of the state estimator are adjusted based on a measured electrocardiographic and/or a measured body-surface-potential signal. The electrical potential of one or more cells is determined based on the one or more adjusted parameters or states. In one aspect of the present technique, one or more representations of an organ comprising the one or more cells is generated such that the electrical potential or its deriving characteristic of the one or more cells is visually indicated.