This study was conducted to directly compare the effects of pulsatile and nonpulsatile blood flow in the extracorporeal circulation upon renal tissue perfusion by using a tissue perfusion measurement system. A total cardiopulmonary bypass circuit was constructed to accommodate twelve Yorkshire swine, weighing 20 approximately 30 kg. Animals were randomly assigned to group 1 (n = 6, nonpulsatile centrifugal pump) or group 2 (n = 6, pulsatile T-PLS pump). A tissue perfusion measurement probe (Q-Flow 500) was inserted into the renal parenchymal tissue, and the extracorporeal circulation was maintained for an hour at a pump flow rate of 2 L/min after aortic cross-clamping. Tissue perfusion flow in the kidney was measured before bypass and every 10 minutes after bypass. Renal tissue perfusion flow was substantially higher in the pulsatile group throughout bypass (ranging 48.5-64.1 ml/min/100 g in group 1 vs. 51.0-88.1 ml/min/100 g in group 2). The intergroup difference was significant at 30 minutes (47.5 +/- 18.3 ml/min/100 g in group 1 vs. 83.4 +/- 28.5 ml/min/100 g in group 2; p = 0.026). Pulsatile flow achieves higher levels of tissue perfusion of the kidney during short-term extracorporeal circulation. A further study is required to observe the effects of pulsatile flow upon other vital organs and its long-term significance.