In one previous study, esCCO was compared with continuous thermodilution CO (TDCO), measurements in 36 postoperative cardiac surgery patients, showing a bias (mean difference) of -0.06 and a precision (1 SD) of 0.82 L/min. In addition, esCCO was compared with intermittent bolus TDCO, showing a correlation coefficient of 0.82 (P < 0.001, n = 24), a bias of -0.63, and a precision of 1.01 L/min (n = 119). The results of clinical use of esCCO suggest that its measurement accuracy is comparable to the thermodilution method in general population. However, no any intraoperative comparison for cardiac surgery patients was reported before. This study is designed for the accuracy in the patients undergoing cardiac surgery.