Objective: Levosimendan (LS) is a new inodilator agent that improves cardiac contractility by increasing the sensitivity of troponin C to calcium, which usage in cardiac surgery has been growing in the recent years. We aimed to determine the best timing of the administration of LS in high-risk patients who underwent cardiovascular surgery. Methods: Fifteen patients were evaluated retrospectively who have left ventricular dysfunction, underwent open-heart surgery and were applied LS in different phases of operation. Patients were divided into 3 groups according to timing of LS. Levosimendan infusion (0. 1 µg-1kg-1min) was applied after the induction of anaesthesia (n=5) (Group 1), during the pump removal period (n=5) (Group 2) and in postoperative period (n=5) (Group 3). Demographic data, operative characteristics, mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), pulmonary wedge capillary pressure (PWCP), cardiac index (CI), inotropic agent consumption, postoperative urine output, lactate levels of groups were compared between before and after LS treatment. Data were evaluated by Fisher exact, Kruskal-Wallis, Mann-Whitney U and Wilcoxon rank tests. Results: In all patients, urine output was satisfactory 24 hours after LS application. There was a significant increase in CI of all 3 groups (p=0.04). Also, there was a significant decrease in PCWP of all 3 groups before and after LS (p=0.04). There was a significant decrease in MPAP in Group 2 and 3 (p=0.04). Twenty- four hours after LS application, whereas all inotropic agents could be stopped in Group 1 and 2, in Group 3 inotropic infusion (dopamine [10 µg-1kg-1min (5-17.5)], dobutamine [15 µg-1kg-1min (5-20)] and adrenaline [0.4 µg-1kg-1min (0.15–0.65)]) couldn’t be stopped (p= 0.007). During postoperative period, in Groups 1 and 2 one case from each required intraaortic balloon pump, while in Group 3 four patients were applied intraaortic balloon pump (p=0.08). Conclusion: According to our experience, LS is effective in high-risk cases during cardiac surgery, especially during the intra-operative and pump removal periods; however, no successful outcomes were observed during the post-operative period. As a result, case selection and timing should be performed well when using LS.