Aim: The LeoDOR trial explored the efficacy and safety of intermittent levosimendan therapy in the vulnerable phase following a hospitalization for acute heart failure (HF). Methods and results: In this prospective multicentre, double-blind, two-armed trial, patients with advanced HF were randomized 2:1 at the end of an index hospitalization for acute HF to intermittent levosimendan therapy or matching placebo for 12 weeks. All patients had left ventricular ejection fraction (LVEF) ≤30% during index hospitalization. Levosimendan was administered according to centre preference either as 6 h infusion at a rate of 0.2 μg/kg/min every 2 weeks, or as 24 h infusion at a rate of 0.1 μg/kg/min every 3 weeks. The primary efficacy assessment after 14 weeks was based on a global rank score consisting of three hierarchical groups. Secondary clinical endpoints included the composite risk of tiers 1 and 2 at 14 and 26 weeks, respectively. Due to the COVID-19 pandemic, the planned number of patients could not be recruited. The final modified intention-to-treat analysis included 145 patients (93 in the combined levosimendan arm, 52 in the placebo arm), which reduced the statistical power to detect a 20% risk reduction in the primary endpoint to 60%. Compared with placebo, intermittent levosimendan had no significant effect on the primary endpoint: the mean rank score was 72.55 for the levosimendan group versus 73.81 for the placebo group (p = 0.863). However, there was a signal towards a higher incidence of the individual clinical components of the primary endpoint in the levosimendan group versus the placebo group both after 14 weeks (hazard ratio [HR] 2.94, 95% confidence interval [CI] 1.12–7.68; p = 0.021) and 26 weeks (HR 1.64, 95% CI 0.87–3.11; p = 0.122). Conclusions: Among patients recently hospitalized with HF and reduced LVEF, intermittent levosimendan therapy did not improve post-hospitalization clinical stability.