Inclusion Criteria:  Left ventricular ejection fraction (LVEF) ≤ 45% Non- negligible pleural effusion by x-ray, ultrasound, CT or MRI, suspected to be due to heart failure Age ≥ 18 years  Exclusion Criteria:  Known or suspected malignant disease Suspected pulmonary or pleural infection (pneumonia symptoms with c- reactive protein>100 mg/L or white blood count>11) Recent (<3 months) intrathoracic procedure (including heart or lung surgery, transcatheter aortic valve implantation (TAVI) or thoracentesis) Contraindications to thoracentesis according to local guidelines (such as spontaneously elevated international normalized ratio (INR) or thrombocytopenia), patients on oral anticoagulation may be randomized. Severe aortic stenosis Massive pleural effusion (equivalent to >2/3 of lung on a standing chest x-ray) Substantially affected hemodynamics (systolic blood pressure < 85mmHg, need of inotropes) or high oxygen demand (>7L/min) Estimated glomerular filtration rate (eGFR) <15ml/min/1.73m2 or acute renal failure Inability to give informed consent