Abstract: A primary fluid actuated, secondary fluid propelling system, suitable for use, for example, as an implantable, artificial heart device, comprises a unidirectional pump for pumping electrorheological fluid, two return loops connected to the pump, and for each return loop, two electrorheological valves therein in series flow, and a primary fluid actuated, secondary fluid propelling device connected to that loop at a position between the two electrorheologocal valves therein. The primary fluid actuated, secondary fluid propelling devices may comprise a casing having the interior thereof divided by a pressure transmitting flexible diaphragm into a first cavity for receiving electrorheological fluid from that return loop, and a second cavity for propelling the secondary fluid. The electrorheological valves are actuated to pressurize one first cavity while emptying the other and vice versa.