A pneumatic pump (50) comprises two coaxial cylindricalpumping chambers (60, 62), each enclosing a piston (54, 56) connectedto the other through a partition (58) by a tube (64), thereby forming amonolithic piston assembly that is driven axially by a common electricalactuator (68) providing reciprocating motion. The volume in the bottomchamber is selected as needed to provide the desired pressure in the leftventricle (34) of an artificial heart (30) driven by the pump (50). Thediameterof the tube (64) connecting the pistons (54, 56) is selected suchthat the stroke volume of the top chamber (60) is reduced with respect tothat of the bottom chamber (62) as needed to match the reduced pressurerequirements of the right ventricle (32) of the artificial heart. Checkvalves (74, 76, 78, 80) are used in each chamber to ensure venting of excesspressure during the blood ejection phase and to limit the vacuumduring the fill phase.
