The objective of this work is to reveal the influence of the experimentally observed passive viscous behaviour of the myocardium on the electromechanical activity by making use of computational approaches. For this purpose, we adopt the fully implicit finite element framework and the passive response is described by the orthotropic viscoelastic material model. The capabilities of the proposed model are assessed by comparing finite element simulations of spiral waves in a heart tissue for the elastic and viscoelastic formulations. The results obtained indicate that rate effects in the passive myocardium play a significant role on the active myocardium response by decreasing the electrical wave speed which consequently effects the evolution of spiral waves. We further investigate the influence of viscosity on the defibrillation phenomenon by means of a three-field coupled finite element formulation of bidomain electromechanics. (C) 2014 The Authors. Published by Elsevier B.V.