Abstract: A cardiac assist device which operates by cyclically exerting pressure through an implanted inflatable sheath, which surrounds the myocardium. The sheath is rigid and encloses a bladder or plurality of bladders into which a fluid, either in the form of an inert gas or a liquid is pulsed, with a time displacement curve similar or identical to the contraction-distension characteristics exhibited normally by the myocardium during a cardiac cycle. Pulsing is triggered by the EKG R-spike of the patient which operates a valve. In order to provide adequate fluid volume for the required pressure through the valve, an elastic fluid reservoir is provided.