Objective To evalute the accuracy of stroke volume variation (SVV) in monitoring blood volume in patients undergoing off-pump coronary artery bypass grafting.Methods Twenty-one ASA Ⅱ or Ⅲ patients of both sexes aged 44-77 yr undergoing off-pump coronary artery bypass grafting were enrolled in this study.Anesthesia was induced with midazolam,etomidate,fentanyl,rocuronium and dolicaine and maintained with target-controlled infusion of propofol,infusion of remifentanil,intermittent iv injetion of atracurium and inhalation of sevoflurane.The patients were mechanically ventilated (VT 8 ml/kg,RR 12 bpm,I:E 1:2,PEEP 0,FiO2 80％ ).PEr CO2 was maintained at 35-44 mm Hg.Radial artery was cannulated and connected to FloTrac pressure transducer and Vigileo monitor.6％ hydroxyethyl starch 130/0.4 sodium chloride solution 7 ml/kg was infused at a rate of 0.25 ml· kg- 1 1· min- 1 at 5 min of haemodynamics stabilization after pericardiotomy (T1).HR,MAP,CVP,systemic vascular resistance (SVR),systemic vascular nesistance index (SVRI),SVV,stroke volume index (SVI)and CI were recorded at T1 and at 10 min after loading dose (T2).The change rate of HR(△HR),MAP(△MAP),CVP(△CVP),SVR(△SVR),SVV(△SVV),SVI(△SVI) and CI(△CI) were calculated.△SVI≥25％ was considered effective volume expansion.The ROC curves for HR,MAP,CVP,SVR and SVV in determining the volume expansion efficacy were plotted.The area under the curves and 95 ％ confidence interval were calculated.Results Compared with T1,CVP,SVI,CO and CI were significantly increased,SVRI and SVV decreased at T2 (P ＜ 0.01).There was no significant difference in MAP and HR between T1 and T2(P ＞0.05).△SVI was negatively correlated with △HR and △SVR ( r =- 0.737,r =- 0.480,P ＜ 0.05).△SVI was not correlated with △CVP,△MAP and( P ＞ 0.05).The change in SVI was determined by SVV 8.8％ (sensitivity =52.6％,specificity =100.0％ ).The area under the curve for SVV and 95％ confidence interval were 0.579(0.346-0.812).Conclusion SVV can not be used to accuratelymonitor the changes in blood volume in patients undergoing off-pump coronary artery bypass grafting.