1. In 12 dogs the right part of the diaphragm was stimulated 4, 5, 8, 11, and 14 weeks by means of a pacemaker. 2. Essential findings have been the increase of the amount of glycogen after 5 weeks, the increase of myofilaments per myofibril after 8 weeks, and the increase in the share of mitochondria in the 11th week. After 14 weeks all values have reached again their initial level as the result of an adaptation. 3. From the quantitative structural findings it can be taken that the diaphragm musculature is not changed by the electrostimulation in such a way that the functional preconditions for covering heart muscle deficiencies by diaphragm flaps are given.