Effect of Dapagliflozin on Submaximal Exercise Tolerance in Heart Failure

Inclusion Criteria:

1. Diagnosis of HFrEF with NYHA Class II-III functional class, which has been present forat least two months
2. Left ventricular ejection fraction ≤ 40%
3. Stable medical therapy for at least 1 month
4. Plasma NT-proBNP level of: ≥ 200pg/mL; OR ≥ 125pg/mL if they were hospitalized for HFwithin the past 12 months; or ≥ 250 pg/mL if patient had atrial fibrillation/flutteron baseline ECG

Exclusion Criteria: 1. Receiving therapy with an SGLT2 inhibitor within 8 weeks prior to enrollment orprevious intolerance of an SGLT2 inhibitor 2. Type 1 diabetes mellitus 3. Age <18 years old 4. Pregnancy: Women of childbearing potential will undergo a urine pregnancy test duringthe screening visit. 5. Uncontrolled atrial fibrillation, as defined by a resting heart rate > 100 beats perminute at the time of the baseline assessment 6. Paroxysmal atrial fibrillation (Afib) or flutter with >1 hour of continuous Afibdocumented within the previous 6 months (prior to screening or randomization),direct-current (DC) cardioversion or ablation procedure for Afib within 6 months, orplan to attempt to restore sinus rhythm (with drug therapy, ablation, or DCcardioversion) within 6 months of randomization. Subjects with persistent Afib and nosinus rhythm documented in the prior 6 months are permitted. 7. Hemoglobin < 10 g/dL 8. eGFR < 25 mL/min/1.73m^2, or unstable or rapidly progressing renal disease at the timeof randomization 9. Subject inability/unwillingness to exercise 10. Greater than moderate left sided valvular disease (mitral regurgitation, aorticstenosis, aortic regurgitation), moderate or greater mitral stenosis, severeright-sided valvular disease 11. Known hypertrophic, infiltrative, restrictive or inflammatory cardiomyopathy 12. Clinically significant pericardial disease, as per investigator judgment 13. Current angina due to clinically significant epicardial coronary disease, as perinvestigator judgment 14. Acute coronary syndrome or coronary intervention within the past 2 months 15. Primary pulmonary artery hypertension (WHO Group 1 Pulmonary Arterial Hypertension) 16. Clinically significant lung disease as defined by: Chronic Obstructive PulmonaryDisease meeting Stage III or greater GOLD criteria (FEV1<50% predicted), treatmentwith oral steroids within the past 6 months for an exacerbation of obstructive lungdisease, current use of supplemental oxygen aside from nocturnal oxygen for thetreatment of obstructive sleep apnea. - Desaturation to <90% on the baseline maximal effort cardiopulmonary exercise testwill also be grounds for exclusion 17. Clinically-significant ischemia, as per investigator's judgement, on stress testingwithout either (1) subsequent revascularization, (2) an angiogram demonstrating theabsence of clinically significant epicardial coronary artery disease, as perinvestigator judgment; (3) a follow-up 'negative' stress test, particularly when usinga more specific technique (i.e., a negative perfusion imaging test following a 'positive' ECG stress test) - Exercise induced regional wall motion abnormalities suggestive of ongoing ischemiaduring the baseline maximal effort cardiopulmonary exercise test will be exclusionary 18. Implantation of a CRT device within 12 weeks prior to enrollment or intent to implanta CRT device during the study period 19. Previous cardiac transplantation or implantation of a ventricular assist device, orimplantation expected after randomization 20. Symptomatic bradycardia or second- or third-degree heart block, in the absence of apacemaker 21. Significant liver disease impacting synthetic function or volume control (ALT/AST > 3xULN, Albumin < 3.0 g/dL) 22. Severe right ventricular dysfunction 23. Baseline resting seated systolic blood pressure > 180 mmHg or <90 mmHg 24. Orthostatic blood pressure response to the transition from supine to standing (>20mmHg reduction in systolic blood pressure 2-3 minutes after standing) 25. Active participation in another study that utilizes an investigational agent (observational studies/registries allowed) 26. Any condition that, in the opinion of the investigator, will interfere with thecompletion of the study. This may include comorbid or psychiatric conditions that mayimpede successful completion of the protocol, or logistical concerns (e.g. inabilityto travel to the exercise unit).