Although beta-blockers are not recommended for the treatment of heart failure with preserved ejection fraction (HFpEF) according to the latest European Society of Cardiology and American Heart Association/American College of Cardiology/Heart Failure Society of America guidelines, these therapies remain commonly used for comorbidity management. There has been concern that beta-blockers may adversely influence clinical outcomes by limiting chronotropic response in HFpEF.This study sought to examine the contemporary use and implications of beta-blockers in patients with heart failure with mildly reduced ejection fraction (HFmrEF) or HFpEF.In the DELIVER (Dapagliflozin Evaluation to Improve the Lives of Patients With Preserved Ejection Fraction Heart Failure) trial, a total of 6,263 patients with symptomatic heart failure (HF) with a left ventricular ejection fraction (LVEF) >40% were randomized to dapagliflozin or placebo across 20 countries. In this prespecified analysis, efficacy and safety outcomes were examined according to beta-blocker use at randomization. The primary outcome was cardiovascular death or worsening HF.Overall, beta-blockers were used in 5,177 patients (83%), with wide variation by geographic region. Beta-blocker use was associated with a lower risk of the primary outcome in covariate-adjusted models (HR: 0.70; 95% CI: 0.60-0.83). Dapagliflozin consistently reduced the risk of the primary outcome in patients taking beta-blockers (HR: 0.82; 95% CI: 0.72-0.94) and in patients not taking beta-blockers (HR: 0.79; 95% CI: 0.61-1.03; Pinteraction = 0.85), with similar findings for key secondary endpoints. Adverse events were balanced between patients randomized to dapagliflozin and placebo, regardless of background beta-blocker use.In patients with HFmrEF or HFpEF who were enrolled in DELIVER, 4 out of 5 participants were treated with a beta-blocker. Beta-blocker use was not associated with a higher risk of worsening HF or cardiovascular death. Dapagliflozin consistently and safely reduced clinical events, irrespective of background beta-blocker use. (Dapagliflozin Evaluation to Improve the Lives of Patients With Preserved Ejection Fraction Heart Failure [DELIVER]; NCT03619213).