It has been shown that unloading of hearts by mechanical cardiac assist devices leads to improvement of the heart's function to variable extent. Improvement fails if the extracellular matrix (ECM) has been remodelled definitively. Thus, the limiting factors for improvement are not the myocytes but the matrix. The goal of these in-vivo experiments is to investigate the effect of electrical microcurrent (MC) on the ECM and as a consequence on healing of heart failure. As previously published, MC is able to modify the myocardium (collagen, MMPs, TIMPs) of spontaneously hypertensive rats (SHR) under in-vitro conditions.