The mechanical properties of diaphragm muscle in dogs were measured. A portion of the diaphragm was isolated and formed into a pouch which in turn was connected to various hydraulic circuits. We measured pressure response to electrical stimulation for various voltages, frequencies and baseline pressures; and also contraction time. Further, we obtained pressure-volume curves and estimated the power output of the actively contracting muscle. From the results we conclude that the properties of the diaphragm muscle do not exclude its use as a myocardial substitute.