The prognostic significance of resting heart rate (HR) in atrial fibrillation (AF) patients with heart failure with reduced ejection fraction (HFrEF) is unclear, and there are no recommendations about the optimal HR in patients with HF in the current guidelines. Thus, we aimed to identify the relationship between resting HR and mortality in AF patients with HFrEF. A prospective multicenter cohort study was conducted between July 2014 and December 2018. We enrolled consecutive 144 AF patients with HFrEF (mean age 75 years, 34% female). The primary endpoint was all-cause death. We compared the outcomes between the high HR group (HR > 81 beats per minute [bpm], interquartile range [IQR] of HR ≥ 67%, n = 50), and the low HR group (HR ≤ 81 bpm, IQR of HR < 67%, n = 94). During a median follow-up of 538 days, the primary endpoint occurred in 41 (28.5%) patients. In Kaplan–Meier analysis, high HR was associated with a progressively increased risk of mortality (log-rank test, p = 0.034). After multivariate Cox regression analysis, high HR predicted all-cause death after adjusting for age, sex, hemoglobin, estimated glomerular filtration rate, LVEF, use of angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, beta-blockers, digoxin, amiodarone, and calcium channel blockers (hazard ratio, 1.979; 95% confidence interval, 1.005–3.898; p = 0.048). Resting HR > 81 bpm at discharge had a significantly higher risk of death compared with HR ≤ 81 bpm in AF patients with HFrEF.