A hydraulic mount apparatus (20) for supporting a vibration source is disclosed. The mount apparatus (20) includes a housing (22) that defines a housing chamber (24) separated by a partition assembly (62) into a pumping chamber (64) and a receiving chamber (66), each containing a magnetorheological fluid (68). A flexible body (48) is partially disposed in the pumping chamber (64) for deforming elastically in response to vibrations caused by an external excitation. A fluid passage (106) extends between the pumping chamber (64) and the receiving chamber (66) for passing the fluid therebetween during low frequency vibrations. A piezostack actuator (118) partially extends into the pumping chamber (64) for moving within the pumping chamber (64) for varying the volume of the pumping chamber (64) to prevent a pressure increase in the pressure chamber to substantially cancel relatively high frequency vibrations.