BACKGROUND : Cardiopulmonary bypass (CPB) is associated with a systemic inflammatory response and an endothelial dysfunction, whose qualitative assessment appears to be a major issue. Endocan (ESM-1, endothelial cell specific molecule-1) is a protein preferentially expressed by the endothelium and previously associated with prognosis of septic shock or acute respiratory distress syndrome. In this pilot study, we investigated the kinetic of Endocan in planned coronary artery bypass grafting (CABG) surgery with CPB. PATIENTS AND METHODS : We conducted an observational, prospective, mono centre study. All adult patients with left systolic ejection fraction>50%, undergoing planned on-pump CABG, were screened for inclusion. A written informed consent was obtained. Measurements and main results Serum Endocan concentrations were respectively 2.4 [2.1-3.0] ng. mL-1, 10.4 [7.4-13.9] ng.mL-1, 5.7 [4.4-8.2] ng.mL-1, and 5.4 [4.1-7.5] ng.mL-1 at day 0, day 1, day 3 and day 5. Endocan concentrations increased at day 1, day 3, and day 5 in comparison with preoperative concentration (P<0.001). In the multivariate analysis, age (P=0.002), history of acute coronary syndrome (P=0.024) and the catecholamine-free days at day 28 (P=0.007) were associated to the increase of perioperative Endocan concentrations. CONCLUSION : Serum Endocan concentration increases after CABG surgery with CPB until day 1. The norepinephrine support increases the risk of Endocan release, suggesting a relationship between the kinetic of Endocan and the vasoplegic syndrome. At day 3, Endocan concentration decreases slowly but is not normalised at day 5. Further studies should investigate the prognostic value of the magnitude of postoperative Endocan concentration after cardiac surgery.