BackgroundHeart failure with reduced ejection fraction (HFrEF) is associated with sleep dyspnea (SDB), which plays an adverse role in the pathophysiology of the condition. SDB management in HFrEF, however, remains controversial. HFrEF’s medical management has recently made significant progress with the discovery of new therapeutic avenues, namely sodia-glucose cotransporter-2 (SGLT-2) inhibitors, and better treatment of co-morbidities. Dapagliflozin, one of the SGLT-2 inhibitors, is a good candidate for correcting SDB of HFrEF patients because their known mechanisms of action are likely to counteract the pathophysiology of SDB in HFrEF.Methods/designThe trial is a 3-month, multicentric, prospective, randomized controlled clinical study. Patients (i.e., adults with left ventricular ejection fraction ≤ 40%, Apnoea–Hypopnoea Index ≥ 15) will be randomized to receive optimized heart failure therapy plus a standard dose of dapagliflozin, while the control group will receive only optimized heart failure therapy. Patients will be evaluated before and after 3 months (nocturnal ventilatory polygraphy, echocardiography, laboratory testing, and quality-of-life and SDB questionnaires). The primary outcome is the change in the Apnoea–Hypopnoea Index, before and after 3 months of treatment.Trial registrationwww.chictr.org.cn, ChiCTR2100049834. Registered 10 August 2021.