Beta 3 Agonist Treatment in Heart Failure

Inclusion Criteria: 1. Stable heart failure NYHA class II-III on ischemic or non-ischemic basis 2. Left ventricular ejection fraction (LVEF) \< 40% 3. Stable sinus rhythm (SR) 4. On optimised evidence-based pharmacological HF treatment stable \> 4 weeks with no current plan for changing HF therapy. The therapy must include a beta-blocker. 5. No change in diuretics \< 4 weeks 6. \>18 years Exclusion Criteria: 1. Unstable cardiac condition 2. Acute myocardial infarction (AMI) or revascularisation \< 3 month ago 3. Atrial fibrillation (for technical reasons in relation to imaging and HR reporting) 4. Uncorrected significant primary obstructive valve disease 5. Planned major surgery including cardiac revascularisation 6. Hemodynamically significant obstructive cardiomyopathy 7. Stroke with significant neurological deficit 8. Acute myocarditis or constrictive pericarditis 9. Symptomatic bradycardia or \> 1. degree AV-block unless the patient has a pacemaker 10. Clinically significant hepatic (transaminases or bilirubin x 3 above upper reference level) or renal (GFR\< 50 ml/min/1,73 m2) diseases 11. Heart failure due to uncorrected thyroid disease 12. Cardiac mechanical support 13. \< 6 months after CRT 14. Uncontrolled hypotension (defined as symptomatic systolic blood pressure \< 90 mmHg) - or hypertension (defined as systolic at 180 mmHg or above and/or diastolic blood pressure at 110 mmHg or below) 15. Body mass index (BMI) \> 35 16. Unable to give informed consent 17. Reduced compliance 18. All women of child bearing potential will be required to use adequate contraception 19. Pregnant or lactating women 20. Treatment with a tricyclic antidepressant or CYP2D6 substrates other than beta-blockers or treatment with digoxin.