The trajectories of systolic function after admission for acute heart failure (HF) and their effect on clinical outcomes have not been fully elucidated. We aimed to assess changes in left ventricular ejection fraction (LVEF) between the index and 1year after discharge and to examine their prognostic implications. We extracted data from a prospective multicentre registry of patients hospitalized for acute HF and identified 1636 patients with LVEF data at admission and 1year after discharge. We categorized them into five groups based on LVEF changes: HF with unchanged-preserved EF [HFunc-pEF (EF≥50%); N=527, 32.2%], unchanged-mildly reduced EF [HFunc-mrEF (EF 41-49%); N=86, 5.3%], unchanged-reduced EF [HFunc-rEF (EF≤40%); N=377, 23.0%], worsened EF (HFworEF; N=83, 5.1%), and improved EF (HFimpEF; N=563, 34.4%). We then evaluated the subsequent composite outcome of cardiovascular death and HF readmission. During 1year after discharge, 53% of patients with HF with reduced EF and 67% of those with HF with mildly reduced EF (HFmrEF) transitioned to other categories, whereas 92% of those with HF with preserved EF (HFpEF) remained within the same category. Patients with HFimpEF were more likely to be younger and had relatively preserved renal function, whereas those with HFworEF were the oldest and had more comorbidities among the five groups. After multivariable adjustment, patients with HFimpEF and HFunc-pEF had a lower risk for composite outcomes when referenced to patients with HFunc-rEF [hazard ratio (95% confidence interval), P-value: 0.28 (0.16-0.49), P<0.001, and 0.40 (0.25-0.63), P<0.001, respectively]. Conversely, patients with HFunc-mrEF and HFworEF had a comparable risk [0.44 (0.18-1.07), P=0.07, and 0.63 (0.29-1.39), P=0.26, respectively]. A substantial number of patients with HF experienced transitions to other categories after discharge. Notably, patients with decreased EF experienced a worse prognosis, even with slight decreases (e.g. HFpEF transitioning to HFmrEF). These findings emphasize the significance of longitudinal assessments of systolic function to better manage patients following acute decompensation.