Background: Positive end-expiratory pressure(PEEP) ventilation causes reduction in cardiac output and increase of intra-thoracic pressure, hence reduction of hepatic blood flow. The purpose of this study is to evaluate the changes of hepatic venous oxygen saturation, tension and content during increase and removal of PEEP and to evaluate hemodynamic variable which has the greatest effect on hepatic oxygenation. Method: Eight dogs were anethetised with 1.0 vol% isoflurane and 100% oxygen. After 30 minutes of stabilization of vital signs, PEEP were increased from 0 cmH2O to 5 cmH2O and 10 cmH2O and lowered to 0 cmH2O again, and hemodynamic data (heart rate, arterial blood pressure, central venous pressure(CVP), pulmonary arterial pressure, pulmonary arterial occlusion pressure and cardiac output(CO)) and hepatic venous oxygenation data (hepatic venous oxygen saturation(ShvO2), tension(PhvO2) and content(ChvO2)) were measured at each step. Results: CO, ShvO2, PhvO2 and ChvO2 decreased significantly at 10 cmH2O PEEP compared to the baseline and 5 cmH2O PEEP and CO, ShvO2 and ChvO2 increased signicantly with removal of PEEP. CVP increased significantly at 10 cmH2O PEEP and decreased significantly with PEEP removal. PEEP showed close correlationship with CO and CVP considering all steps of PEEP and PEEP removal. ShvO2 and PhvO2 showed most close correlationship with CO considering all steps of PEEP and PEEP removal. Conclusion: ShvO2 with PEEP therapy is dependent upon CO. Therefore cardiac output maintenance is essential during PEEP therapy. For exact evaluation of hepatic oxygenation, it is valuable to monitor ShvO2.