Background: Type 2 diabetes and prediabetes are risk factors for heart failure and adverse heart failure outcomes. The Dapagliflozin Evaluation to Improve the Lives of Patients with Preserved Ejection Fraction Heart Failure (DELIVER) trial showed that dapagliflozin was associated with a reduction in the primary outcome of worsening heart failure or cardiovascular mortality in patients with heart failure with mildly reduced or preserved ejection fraction. We aimed to assess the efficacy and safety of oral dapagliflozin in these patients by their baseline glycaemia categories., Methods: DELIVER was an international, multicentre, double-blind, randomised, placebo-controlled trial done in 350 health-care centres and hospitals across 20 countries. Patients aged 40 years or older with New York Heart Association class II-IV, left ventricular ejection fraction of more than 40%, elevated natriuretic peptides (N-terminal pro B-type natriuretic peptide ≥300 pg/mL or ≥600 pg/mL for patients in atrial fibrillation or flutter), and evidence of structural heart disease were randomly assigned (1:1) to 10 mg dapagliflozin or placebo, administered orally, and followed up for a median of 2·3 years (IQR 1·7-2·8). The primary outcome, a composite of time from randomisation to first worsening heart failure events (defined as an unplanned hospitalisation or urgent heart failure visit requiring intravenous therapy) or cardiovascular death, in participants with type 2 diabetes (history of or identified by HbA 1c ≥6·5% [48 mmol/mol] at baseline) or prediabetes (HbA 1c 5·7 to <6·5% [39 mmol/mol to <48 mmol/mol] at baseline) was compared with those with normoglycaemia (HbA 1c <5·7% [39 mmol/mol]). Efficacy of dapagliflozin versus placebo was assessed according to glycaemic status and based on HbA 1c as a continuous measure. The full-analysis set comprised all patients who were randomly assigned to study treatment, with patients analysed according to their randomised treatment assignment, irrespective of the treatment received (ie, intention to treat). The safety analysis set comprised patients who were randomly assigned to study treatment and who took at least one dose of investigational product, with patients analysed according to the treatment actually received. This trial is registered with ClinicalTrials.gov, NCT03619213., Findings: Between Sept 1, 2018, and Jan 18, 2021, 6263 patients were randomly assigned to oral dapagliflozin (n=3131) or placebo (n=3132). Of these patients, 1175 had normoglycaemia, 1934 had prediabetes, and 3150 had type 2 diabetes and were included in the glycaemia subgroup analysis (3515 [56·2%] of 6263 patients were men and 4435 [70·9%] were White). The incidence rate of the primary outcome was 6·9 per 100 patient-years in the normoglycaemia subgroup (reference), increasing to 7·6 per 100 patient-years in the prediabetes subgroup (hazard ratio 1·09 [95% CI 0·90-1·31]) and 10·1 per 100 patient-years in the type 2 diabetes subgroup (1·46 [1·24-1·73]; p<0·0001 for trend). Dapagliflozin reduced the risk of the primary outcome versus placebo in each subgroup (hazard ratio 0·77 [95% CI 0·57-1·04], log-rank p=0·088, for patients with normoglycaemia, 0·87 [0·69-1·08], log-rank p=0·21, for patients with prediabetes, and 0·81 [0·69-0·95], log-rank p=0·0077, for patients with type 2 diabetes; p interaction =0·82) and across the continuous HbA 1c range (p interaction =0·85). Volume-related or renal serious adverse events or adverse events leading to discontinuation of the study drug, hypoglycaemia, and amputations were not differentially affected by treatment in any of the glycaemia categories., Interpretation: In patients with heart failure with mildly reduced or preserved ejection fraction, oral dapagliflozin improved heart failure outcomes to a similar extent in three glycaemia subgroups: normoglycaemia, prediabetes, and type 2 diabetes. Moreover, the heart failure benefits of dapagliflozin seem to be consistent across a continuous glycaemic range., Funding: AstraZeneca., Competing Interests: Declaration of interests SEI has served on clinical trial committees or as a consultant to AstraZeneca, Boehringer Ingelheim, Novo Nordisk, Merck, Pfizer, Bayer, Abbott, Lexicon Pharmaceuticals, vTv Therapeutics, and Esperion, and has delivered lectures sponsored by AstraZeneca and Boehringer Ingelheim. BLC has received consulting fees from Boehringer Ingelheim. MV has received research grant support or served on advisory boards for American Regent, Amgen, AstraZeneca, Bayer, Baxter Healthcare, Boehringer Ingelheim, Cytokinetics, Lexicon Pharmaceuticals, Novartis, Pharmacosmos, Relypsa, Roche Diagnostics, and Sanofi; received speaker fees from AstraZeneca, Novartis, and Roche Diagnostics; and participates on clinical trial committees for studies sponsored by Galmed, Novartis, Bayer, Occlutech, and Impulse Dynamics. ASD has received research grants (to his institution) from Abbott, AstraZeneca, Alnylam, Bayer, and Novartis, and consulting fees or honoraria from Abbott, Alynylam, AstraZeneca, Axon Therapeutics, Biofourmis, Boston Scientific, Bayer, Cytokinetics, GlaxoSmithKline, Lupin Pharma, Merck, Medpace, Novartis, Parexel, Regeneron, Roche, and Verily. PSJ's employer has been remunerated by AstraZeneca, Bayer, and Novo Nordisk for clinical trial work. PSJ also reports consulting and speaker fees from Novartis, AstraZeneca, and Boehringer Ingelheim; and research funding from Boehringer Ingelheim. RAdB has received research grants from AstraZeneca, Abbott, Boehringer Ingelheim, Cardior Pharmaceuticals, Ionis Pharmaceuticals, Novo Nordisk, and Roche, and has received speaker fees from Abbott, AstraZeneca, Bayer, Bristol Myers Squibb, Novartis, and Roche. AFH has received research grants from American Regent, Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Merck, Novartis, Somologic, and Verily, and has served as a consultant or on the advisory board for Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Cytokinetics, Eidos, Intercept, Merck, and Novartis. MNK reports research grant support from AstraZeneca and Boehringer Ingelheim, and consulting fees from Alnylam, AstraZeneca, Amgen, Bayer, Boehringer Ingelheim, Cytokinetics, Esperion, Eli Lilly, Janssen, Lexicon, Merck (Diabetes and Cardiovascular), Pharmacosmos, Novo Nordisk, Sanofi, and Vifor. CSPL is supported by a Clinician Scientist Award from the National Medical Research Council of Singapore; has received research support from Bayer and Roche Diagnostics; has served as consultant or on the advisory board, steering committee, or executive committee for Actelion, Alleviant Medical, Allysta Pharma, Amgen, AnaCardio AB, Applied Therapeutics, AstraZeneca, Bayer, Boehringer Ingelheim, Boston Scientific, Cytokinetics, Darma, EchoNous, Eli Lilly, Impulse Dynamics, Ionis Pharmaceutical, Janssen Research & Development, Medscape/WebMD Global, Merck, Novartis, Novo Nordisk, Prosciento, Radcliffe Group, Roche Diagnostics, Sanofi, Siemens Healthcare Diagnostics, and Us2.ai; and is a co-founder of and serves as and non-executive director of Us2.ai. FM has received personal fees from AstraZeneca. SJS reports research grants from the US National Institutes of Health, Actelion, AstraZeneca, Corvia, Novartis, and Pfizer, and consulting fees from Abbott, Actelion, AstraZeneca, Amgen, Aria CV, Axon Therapies, Bayer, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Cardiora, Coridea, CVRx, Cyclerion, Cytokinetics, Edwards Lifesciences, Eidos, Eisai, Imara, Impulse Dynamics, Intellia, Ionis, Ironwood, Lilly, Merck, MyoKardia, Novartis, Novo Nordisk, Pfizer, Prothena, Regeneron, Rivus, Sanofi, Shifamed, Tenax, Tenaya, and United Therapeutics. SV reports receiving research grants or speaking honoraria from Amarin, Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Eli Lilly, EOCI Pharmacomm, HLS Therapeutics, Janssen, Novartis, Novo Nordisk, Pfizer, PhaseBio, Sanofi, Sun Pharmaceuticals, and the Toronto Knowledge Translation Working Group. JFKS has received grants or fees for working on clinical trials, consultancy, advisory board or steering committee membership, and other activities from AstraZeneca, Novo Nordisk, Bayer, Boehringer Ingelheim, Novartis, Merck Sharp & Dohme, and Janssen. OB, MP, and AML are employees of AstraZeneca. JJVM has received funding to his institution for his work on clinical trials, consulting, and other activities from Alnylam, Amgen, AstraZeneca, Bayer, Bristol Myers Squibb, Cardurion, Cytokinetics, GlaxoSmithKline, Novartis, Pfizer, and Theracos, and has received personal lecture fees from the Corpus, Abbott, Hickma, Sun Pharmaceuticals, and Medsca. SDS has received research grants from Actelion, Alnylam, Amgen, AstraZeneca, Bellerophon, Bayer, Bristol Myers Squibb, Celladon, Cytokinetics, Eidos, Gilead, GlaxoSmithKline, Ionis, Lilly, Mesoblast, MyoKardia, US National Heart, Lung, and Blood Institute (National Institutes of Health), Neurotronik, Novartis, NovoNordisk, Respicardia, Sanofi Pasteur, Theracos, and Us2.ai; and has consulted for Abbott, Action, Akros, Alnylam, Amgen, Arena, AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Cardior, Cardurion, Corvia, Cytokinetics, Daiichi-Sankyo, GlaxoSmithKline, Lilly, Merck, Myokardia, Novartis, Roche, Theracos, Quantum Genomics, Cardurion, Janssen, Cardiac Dimensions, Tenaya, Sanofi-Pasteur, Dinaqor, Tremeau, CellProThera, Moderna, American Regent, and Sarepta., (Copyright © 2022 Elsevier Ltd. All rights reserved.)