Monodomain model  The monodomain model is a reduction of the bidomain model of the electrical propagation in myocardial tissue. The reduction comes from assuming that the intra- and extracellular domains have equal anisotropy ratios. Although not as physiologically accurate as the bidomain model, it is still adequate in some cases, and has reduced complexity. Beeing formula_1 the domain boundary of the model, the monodomain model can be formulated as follows  where formula_3 is the intracellular conductivity tensor, formula_4 is the transmembrane potential, formula_5 is the transmembrane ionic current per unit area, formula_6 is the membrane conductivity per unit area, formula_7 is the intra- to extracellular conductivity ratio, and formula_8 is the membrane surface area per unit volume (of tissue). The monodomain model can be easily derived from the bidomain model. This last one can be written as  Assuming equal anisotropy ratios, i.e. formula_10, the second equation can be written as  Then, inserting this into the first bidomain equation gives the unique equation of the monodomain model  Differently from the bidomain model, usually the monodomain model is equiped with an isoltad boundary condition, which means that it is assumed that there is not current that can flow from or to the domain (usually the heart). Mathematically, this is done imposing a zero transmembrane potential flux, "i.e.": where formula_14 is the unit outward normal of the domain and formula_15 is the domain boundary.