Acetazolamide in Decompensated Heart Failure With Volume OveRload (ADVOR)

Inclusion Criteria: * Signed written informed consent must be obtained before any study assessment is performed * Male or female patients 18 years of age or older * An elective or emergency hospital admission with clinical diagnosis of decompensated HF with at least one clinical sign of volume overload (e.g. oedema (score 2 or more), ascites confirmed by echography or pleural effusion confirmed by chest X-ray or echography) * Maintenance therapy with oral loop diuretics at a dose of at least 1 mg bumetanide or an equivalent dose for at least 1 month before hospital admission (Conversion: 1 mg bumetanide = 40 mg furosemide = 20 mg torsemide) * Plasma NT-proBNP levels \>1000 ng/mL or BNP levels \>250 ng/mL at the time of screening. * Assessed LVEF by any imaging technique; i.e. echocardiography, catheterization, nuclear scan or magnetic resonance imaging within 12 months of inclusion Exclusion Criteria: * Concurrent diagnosis of an acute coronary syndrome defined as typical chest pain in addition to a troponin rise above the 99th percentile and/or electrocardiographic changes suggestive of cardiac ischemia * History of congenital heart disease requiring surgical correction * History of a cardiac transplantation and/or ventricular assist device * Systolic blood pressure \<90 mmHg or mean arterial pressure \<65 mmHg at the moment of admission * Expected use of intravenous inotropes, vasopressors or nitroprusside during the study. Use of nitrates is allowed only if the patient's systolic blood pressure is \>140 mmHg * Estimated glomerular filtration rate \<20 mL/min/1.73m² at screening * Use of renal replacement therapy or ultrafiltration at any time before study inclusion * Treatment with acetazolamide during the index hospitalization and prior to randomization * Exposure to nephrotoxic agents (i.e. contrast dye) anticipated within the next 3 days * Use of any non-protocol defined diuretic agent with the exception of mineralocorticoid receptor antagonists. Thiazides, metolazone, indapamide and amiloride should be stopped upon study inclusion. If patient is taking a combination drug including a thiazide-type diuretic, the thiazide-type diuretic should be stopped * Current use of sodium-glucose transporter-2 inhibitors * Subjects who are pregnant or breastfeeding