A pump system is described which is particularly suited for use as a left ventricular assist device for internal use in humans. The pump system generally includes a pump having a deformable sac formed in a seamless piece of flexible resilient material having (i) a pair of opposite substantially planar walls and of substantially circular shape joined by an annular wall of substantially semicircular cross-section and (ii) inlet and outlet means. The inlet means have an asymmetric tapered section positioned to direct the inlet flow toward the annular wall of the sac to produce a smooth circular flow within the sac and minimize thrombus formation. A pair of pusher plates are disposed on opposite sides of the sac. Each of the pusher plates are engageable with a respective one of the planar walls of the sac for displacing at least one of the planar walls toward the other to deform the sac. The pump system also includes removable inlet and outlet conduit means with valve means for controlling inlet and outlet flow. Each of the conduit means include connecting means having sealing means for securing the inlet and outlet conduit means to the pump.
