Some studies have been performed to assess the effects of levosimendan on cardiac function when administered to cardiac surgery patients with low cardiac output syndrome (LCOS) in the immediate postoperative period. Levosimendan is an inotropic agent for the treatment of low cardiac output syndrome that seems to have a protective effect on renal function. It is a quasi-experimental study. A total of 100 patients with LCOS received either beta-agonists or levosimendan. We assessed the incidence of postoperative kidney failure in cardiac surgery patients. In patients who had kidney failure at diagnosis of LCOS, we examined whether differences existed in the evolution of kidney failure based on the treatment administered for LCOS. The parameters measured included haemodynamics, oxygen supply, and renal function as assessed by the AKI scale. ANOVA, Student's t-test and Wilcoxon or Friedman tests were used. Up to 30% of cardiac surgery patients had kidney failure at diagnosis of LCOS. Kidney failure at discharge from the ICU was more frequent in patients who received beta-agonist drugs as compared to those who received levosimendan (p < 0.05). The incidence of kidney failure decreased with the postoperative administration of levosimendan to cardiac surgery patients with LCOS, as compared to beta-agonists. Current Controlled Trials ISRCTN 46058317. Date of registration: 7/10/2019. Retrospectively registered.