A microcomputer based system is described that controls the operation of a dual chamber, diaphragm-type pneumatic blood pump in both open-loop and closed-loop modes. The open-loop mode of operation allows selection of pumping rate and systolic time parameters. The closed-loop mode of operation allows selection of pumping rate and pump output parameters, with the systolic time parameter adjusted automatically to maintain a selected pump output in spite of load changes. Digital display of all pump operating parameters is provided. A description of the device and the control techniques employed, the interface circuitry and software algorithm developed, a calibration and tuning procedure, and closed-loop response curves are included. / Master of Science