BackgroundLittle research has been done on ischemic outcomes related to left ventricular ejection fraction (EF) in acute decompensated heart failure (ADHF).MethodsA retrospective cohort study was conducted between 2001 and 2021 using the Chang Gung Research Database. ADHF Patients discharged from hospitals between January 1, 2005, and December 31, 2019. Cardiovascular (CV) mortality and heart failure (HF) rehospitalization are the primary outcome components, along with all-cause mortality, acute myocardial infarction (AMI) and stroke.ResultsA total of 12,852 ADHF patients were identified, of whom 2,222 (17.3%) had HFmrEF, the mean (SD) age was 68.5 (14.6) years, and 1,327 (59.7%) were males. In comparison with HFrEF and HFpEF patients, HFmrEF patients had a significant phenotype comorbid with diabetes, dyslipidemia, and ischemic heart disease. Patients with HFmrEF were more likely to experience renal failure, dialysis, and replacement. Both HFmrEF and HFrEF had similar rates of cardioversion and coronary interventions. There was an intermediate clinical outcome between HFpEF and HFrEF, but HFmrEF had the highest rate of AMI (HFpEF, 9.3%; HFmrEF, 13.6%; HFrEF, 9.9%). The AMI rates in HFmrEF were higher than those in HFpEF (AHR, 1.15; 95% Confidence Interval, 0.99 to 1.32) but not in HFrEF (AHR, 0.99; 95% Confidence Interval, 0.87 to 1.13).ConclusionAcute decompression in patients with HFmrEF increases the risk of myocardial infarction. The relationship between HFmrEF and ischemic cardiomyopathy, as well as optimal anti-ischemic treatment, requires further research on a large scale.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12872-023-03286-9.