This work is focused on different aspects within the loop of multiscale modeling:§On the cellular level, effects of adrenergic regulation and the Long-QT syndrome have been investigated.§On the organ level, a model for the excitation conduction system was developed and the role of electrophysiological heterogeneities was analyzed.§On the torso level a dynamic model of a deforming heart was created and the effects of tissue conductivities on the solution of the forward problem were evaluated.