The coupling between cardiac mechanics and electric signalling can be addressed in a two possible alternative framework: the electrical potential dictates the active stress or the active strain. In this talk the explore the second (less popular) strategy, obtained thanks a factorization of the deformation tensor. After rewriting the equations in a deforming domain, we prove that neglecting the deformation of the substrate induces a non-negligible error in predicting celerity and width of the pulse, while the amplitude and the stability conditions are not affected by the electro--mechanical decoupling. Exact solutions of travelling front type can be found with explicit form of the celerity and steepness. The role of visco-elasticity and the characterization of unstable initial conditions are discussed with the support of numerical simulations, both in one and two spatial dimensions.
