Background: Low cardiac output syndrome (LCOS) after cardiac surgery usually requires inotropes. In this setting, critical illness-related corticosteroid insufficiency (CIRCI) may develop. We aimed to investigate the clinical features of CIRCI in the presence of LCOS and to assess the efficacy of steroid treatment. Methods: We reviewed 28 patients who underwent a rapid adrenocorticotropic hormone (ACTH) test due to the suspicion of CIRCI between February 2010 and September 2014. CIRCI was diagnosed by a change in serum cortisol of <9 μg/dL after the ACTH test or a random cortisol level of <10 μg/dL. Results: Twenty of the 28 patients met the diagnostic criteria. The patients with CIRCI showed higher Sequential Organ Failure Assessment (SOFA) scores than those without CIRCI (16.1±2.3 vs. 11.4±3.5, p=0.001). Six of the patients with CIRCI (30%) received glucocorticoids. With an average elevation of the mean blood pressure by 22.2±8.7 mm Hg after steroid therapy, the duration of inotropic support was shorter in the steroid group than in the non-steroid group (14.1±2.3 days versus 30±22.8 days, p=0.001). Three infections (15%) developed in the non-steroid group, but this was not a significant between-group difference. Conclusion: CIRCI should be suspected in patients with LCOS after cardiac surgery, especially in patients with a high SOFA score. Glucocorticoid replacement therapy may be considered to reduce the use of inotropes without posing an additional risk of infection.