Aims: To investigate the relationship between heart rate and outcomes in heart failure and reduced ejection fraction (HFrEF) patients in sinus rhythm (SR) and atrial fibrillation (AF) adjusting for natriuretic peptide concentration, a powerful prognosticator. Methods and results: Of 13 562 patients from two large HFrEF trials, 10 113 (74.6%) were in SR and 3449 (25.4%) in AF. The primary endpoint was the composite of cardiovascular death or heart failure hospitalization. Heart rate was analysed as a categorical (tertiles, T1–3) and continuous variable (per 10 bpm), separately in patients in SR and AF. Outcomes were adjusted for prognostic variables, including N-terminal prohormone of B-type natriuretic peptide (NT-proBNP), and also examined using change from baseline heart rate to 1 year (≤ −10 bpm, ≥ +10 bpm, < ±10 bpm). SR patients with a higher heart rate had worse symptoms and quality of life, more often had diabetes and higher NT-proBNP concentrations. They had higher risk of the primary endpoint [T3 vs. T1 adjusted hazard ratio (HR) 1.50, 95% confidence interval (CI) 1.35–1.66; P < 0.001; per 10 bpm: 1.12, 95% CI 1.09–1.16; P < 0.001]. In SR, heart rate was associated with a relatively higher risk of pump failure than sudden death (adjusted HR per 10 bpm 1.17, 95% CI 1.09–1.26; P < 0.001 vs. 1.07, 95% CI 1.02–1.13; P = 0.011). Heart rate was not predictive of any outcome in AF. Conclusions: In HFrEF, an elevated heart rate was an independent predictor of adverse cardiovascular outcomes in patients in SR, even after adjustment for NT-proBNP. There was no relationship between heart rate and outcomes in AF. Clinical Trial Registration: ClinicalTrials.gov Identifiers NCT01035255 and NCT00853658.