A ventricle assist device for placement within a living body and including a self contained drive motor for generating pumping action with respect to a hydraulic pumping fluid. The ventricle assist device includes a ventricle having a blood chamber and a pumping chamber and an interconnect means coupled to the pumping chamber of the ventricle for receiving and displacing hydraulic fluid. A separate volume displacement chamber is attached to the interconnect means and provides a reservoir for excess hydraulic fluid for storage during diastole. A fluid pump and drive motor is positioned within the volume displacement chamber and connected at the interconnect means to supply the required pumping action for transfer of hydraulic fluid to and from the pumping chamber. Placement of the fluid pump and drive motor within the volume displacement chamber provides enhanced dissipation of heat from the energy conversion system and improved performance and durability.