The aim of this study was to investigate the ability of PPV to predict fluid responsiveness during displacement of the heart in patients undergoing off-pump coronary artery bypass surgery. After anesthesia, we will measure mean arterial pressure, heart rate, central venous pressure, mean pulmonary artery pressure, pulmonary arterial occlusion pressure, mixed venous oxygen saturation, PPV and cardiac index in patients receiving elective OPCAB. All parameters will be recorded at 5 minutes after the left anterior descending artery anastomosis, immediately after the displacement of the heart for the left circumflex artery anastomosis, and 10 minutes after fluid loading with hydroxyethyl starch 6%(10 mL/kg). Patients whose cardiac index increased by >15% to fluid loading will be defined as responders. To test the abilities of central venous pressure, pulmonary artery occlusion pressure and PPV to predict fluid responsiveness during heart displacement, areas under the receiver operating characteristics curves of the responders will be calculated and compared.