Abstract: A pulsatile blood circulating pump system that is adapted for use in cardiopulmonary bypass, ventricular assist (LVAD, RVAD, BiVAD), ECMO, organ preservation, fetal cardiac bypass, cancer treatment, and various areas of circulation research, which can be controlled in such a way as to produce a desired blood flow that closely approximates the physiological blood flow of the patient. The pump system includes a pulsating mechanism having a housing defining a chamber within which a compressible-expandable bladder is sealably mounted. The system further includes a hydraulic actuator having a pressure imparting member that acts upon a pressure transmissive fluid contained within the actuator chamber in a manner to generate a pulsatile pressure on the transmissive fluid, which, in turn, results in a pulsatile pressure being exerted on bladder in a manner to controllably vary the volume thereof.