Abstract: A pump assembly is disclosed which includes a pump which is externally controlled to vary with time the volume and/or the pressure of fluid pumped therethrough. A memory unit is programmed to provide a desired volume-time and/or pressure-time characteristic. The output of the memory is utilized to drive the pump to provide the aforementioned pump characteristics. Provision is made for appropriately modifying the stored program in accordance with preselected parameters so that the pump can, for example, operate in conjunction with an artificial heart.