Mammals seem to be able to adapt to nonpulsatile circulation. For chronic support, pressure and flow, not the presence of a pulse, are the major requirements to sustain normal organ function. Pulsatile flow, however, seems to offer advantages over nonpulsatile flow for acute support in maintaining lymphatic flow, decreasing systemic vascular resistance, improving peripheral and pulmonary capillary perfusion, and reversing shock. These advantages may not be seen with chronic support with adaptation to nonpulsatile flow. ASAIO Journal 1999; 45:119–122.