BACKGROUND: Hydroxyethyl starch (HES) effectively restores plasma volume and thereby enhances microcirculation and tissue oxygenation at the expense of coagulation impairment. These effects are related to molecular weight, substitution and C2:C6 ratio. But, most of the studies regarding coagulation impairment in cardiac surgeries were performed in patients undergoing cardiopulmonary bypass which significantly causes coagulation derangements. Therefore, we have evaluated the effects of 2 different HES solutions on tissue oxygenation and postoperative bleeding in patients undergoing off-pump coronary artery bypass surgery (OPCAB). METHODS: Forty four patients were prospectively enrolled. After the induction of anesthesia, either HES 130/0.4 (V group) or 200/0.5 (H group) were infused for fluid therapy to maintain predetermined urine output, cardiac index and filling pressure up to 16 h after the surgery. Tissue oxygenation profiles and respiratory parameters were recorded after induction of anesthesia, completion of distal anastomosis and sternum closure, upon admission at intensive care unit, and 4 h thereafter. The amounts of chest tube drainage, transfusion and fluid balance were measured up to 16 h after the surgery. RESULTS: Patients' demographic data were similar between the groups. Tissue oxygenation profiles, respiratory parameters, hemodynamics, and time to extubate were not different between the groups. However, chest tube drainage and transfusion requirements were significantly less in the V group. CONCLUSIONS: In OPCAB, 6% HES 130/0.4 causes less postoperative bleeding and transfusion requirement and has a comparable efficacy on hemodynamic stability, pulmonary function and tissue oxygenation when compared to 6% HES 200/0.5.