Beta 3 Agonist Treatment in Heart Failure-2

Inclusion Criteria: 1. Stable heart failure NYHA class III-IV on ischemic or non-ischemic basis 2. Left ventricular ejection fraction (LVEF) \< 35% as assessed by cardiac CT 3. NT proBNP \> 1000 pg/ml 4. On optimised evidence-based pharmacological HF treatment stable ≥2 weeks with no current plan for changing HF therapy. The therapy must include a beta-blocker. 5. No change in diuretics ≤1 week 6. No admittances to hospital for treatment with intravenously administered positive inotropic agents ≤ 4 weeks. 7. \>18 years Exclusion Criteria: 1. Acute myocardial infarction (AMI) or revascularisation \< 3 month ago 2. Uncorrected significant primary obstructive valve disease 3. Planned major surgery including cardiac revascularisation 4. Hemodynamically significant obstructive cardiomyopathy 5. Acute myocarditis or constrictive pericarditis 6. Clinically significant hepatic (transaminases or bilirubin x 3 above upper reference level) or renal (GFR\< 30 ml/min/1,73 m2) diseases 7. Heart failure due to uncorrected thyroid disease 8. Cardiac mechanical support 9. \< 6 months after CRT 10. Uncontrolled hypotension (defined as symptomatic systolic blood pressure \< 80 mmHg) - or hypertension (defined as systolic at 180 mmHg or above and/or diastolic blood pressure at 110 mmHg or below) 11. Unable to give informed consent 12. Reduced compliance 13. All women of child bearing potential will be required to use adequate contraception 14. Pregnant or lactating women 15. Treatment with a tricyclic antidepressant or CYP2D6 substrates other than beta-blockers or treatment with digoxin. 16. Known allergy to iodine containing contrast 17. Estimated GFR \< 30 ml/min/1.73 m2 18. Congenital or drug induced QT prolongation