Pulsatile and nonpulsatile blood flow have been intensely studied for cardiopulmonary bypass (CPB), isolated organ perfusion, and myocardial preservation. Although early studies differed, later ones have shown the benefits of pulsatile flow. Kidney function, lymph flow, and oxygen consumption are increased during pulsatile perfusion. Also, nonpulsatile CPB increases total peripheral resistance and mean arterial pressure, which are related to time of perfusion. Theories to account for the superiority of pulsatile flow include: (1) "vascular shocks" causing physical displacement of tissues, which changes the boundary layer of interstitial fluid around cell membranes and enhances diffusion ;(2) increased lymph movement during pulsatile flow; and (3) pulsatile energy ensuring the patency of the vascular beds and preventing shunting. New methods to create pulsatile flow and their adaptation to the standard roller pump are discussed.