We retrospectively evaluated the initial clinical experience of intraoperative cardiac output measurement by a new arterial pressure-based cardiac output (APCO:FloTrac/Vigileo) analysis in patients undergoing open heart surgery. Thirty-two patients (mean age 76.4, range 59 to 90)who underwent cardiac surgery under cardiopulmonary bypass( CPB) from July 2008 to September 2009 in our institute were enrolled in this study. There were 14 women and 18 men. The cardiac operations included 28 valve surgeries and 4 coronary artery bypass grafting. The APCO was introduced initially, then a continuous cardiac output (CCO:Swan-Ganz catheter) analysis system was established following the induction of anesthesia. The correlation of both cardiac output measurements was evaluated at 5 time points, T1:induction of anesthesia, T2:sternotomy, T3:after weaning from CPB, T4:closure of the chest, and T5:arrival at intensive care unit. There were no serious complications related to APCO and CCO. The correlation between APCO and CCO was evaluated by Bland-Altman plot analysis. The percentages of correlation between both groups were T1:81.2%, T2:78.1%, T3:59.4%, T4:62.5%, and T5:65.6%. A good correlation was shown in all 6 patients with atrial fibrillation at T1 and T2. No correlation was shown in the 3 patients with left ventricular( LV) dysfunction below LVEF 40%, 1 case at T3, all 3 cases at T4, and 2 cases at T5. Before the institution of CPB, 3 of the 6 at T1 and 3 of the 7 at T2 in whom no correlation was shown, had severe aortic valve insufficiency (AVI).From these results, APCO appears to be an acceptable device to evaluate the intraoperative cardiac output measurement compared with CCO, except in patients with LV dysfunction or AVI at some time points. Further studies will be necessary to elucidate the precise clinical evidence to assess the efficacy of this new analysis device.