Bidomain equations are the standard way to model the electric potential in cardiac tissue. We propose the modification of this model for the case of the diseased heart, e.g. fibrosis of the heart tissue. On microscale, we assume to have periodic diffusive inclusions embedded in the healthy tissue modelled by the bidomain equations. We derive the macroscale model using the homogenisation technique. We recover a bidomain model with modified conductivities, that depend on the volume fraction of the diffusive inclusions but also on their geometries.