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Aims: To evaluate the effects of digoxin in patients with the newly described phenotype of heart failure (HF) and mid-range ejection fraction (HFmrEF), attributed to mild left ventricular systolic dysfunction.Methods and Results: We carried out a retrospective analysis of the Digitalis Investigation Group (DIG) trial which had 7788 patients available for analysis with a left ventricular ejection fraction (LVEF) ranging between 3% and 85%. We compared the effect of digoxin to placebo in three mutually exclusive groups of patients defined by LVEF category: <40% (HF with reduced LVEF, HFrEF, n = 5874), 40-49% (HFmrEF, n = 1195) and ≥50% (HF with preserved LVEF, HFpEF, n = 719). The primary outcome was the composite of cardiovascular death or HF hospitalisation. Patients with HFmrEF resembled patients with HFrEF, more than those with HFpEF, with respect to age, sex and aetiology but were more like HFpEF patients with respect to blood pressure and the prevalence of hypertension. Event rates in patients with HFmrEF were similar to those in HFpEF and much lower than in HFrEF. Digoxin reduced the primary endpoint in patients with HFrEF, mainly due to reduced HF hospitalisation: the digoxin/placebo hazard ratio (HR) for HF hospitalisation was 0.71 [95% confidence interval (CI) 0.65-0.77]. The digoxin/placebo HR for HF hospitalisation in patients with HFmrEF was 0.80 (95% CI 0.63-1.03) and 0.85 (95% CI 0.62-1.17) in those with HFpEF. The digoxin/placebo HR for the composite of HF death or HF hospitalisation was 0.74 (95% CI 0.68-0.81) in HFrEF, 0.83 (95% CI 0.66-1.05) in HFmrEF and 0.88 (95% CI 0.65-1.19) in HFpEF.Conclusions: In this study, event rates in patients with HFmrEF were closer to those in HFpEF than HFrEF. Digoxin had most effect on HF hospitalisation in patients with HFrEF, an intermediate effect in HFmrEF, and the smallest effect in HFpEF. [ABSTRACT FROM AUTHOR]