To assess the effect of Empagliflozin on cardiac biomarkers, cardiac function at rest and during stress, cardiac hemodynamics, renal function, metabolism, daily activity level and health-related quality of life in stable, symptomatic heart failure patients with reduced left ventricular ejection fraction.

The primary hypothesis is that 3 months' treatment with Empagliflozin 10 mg a day will reduce the plasma concentrations of N-terminal pro-brain natriuretic peptide (NT-proBNP).

Inclusion Criteria:

• Optimal Heart Failure Therapy in accordance with European and National Guidelines
• LVEF ≤ 0.40
• eGFR > 30 ml/min/1.73 m2
• BMI < 45 kg/m2
• NYHA class I-III
• Age > 18 years
• If T2D - optimal treatment in accordance with European and National Guidelines
• If T2D - stable doses of antiglycemic treatment for 30 days
• If T2D - HbA1C 6.5-10%

Exclusion Criteria:

• CRT-D/-P implanted < 90 days
• Uncorrected severe valvular disease
• Non-compliance
• Use of metalozone
• NYHA IV
• Age > 85 years
• Dementia
• Admission for HF < 30 days
• Admission for hypoglycemia < 12 month
• Known sustained VT
• Symptomatic hypotension and systolic BP < 95 mmHg
• Unable to perform an exercise test
• Immobilization
• Pregnancy
• Participation in other medical trials
• Previous intolerance of Empagliflozin or excipients