Inclusion Criteria:

• Aged 18 years or older.
• Diagnosed with Acute Decompensated Heart Failure (ADHF), with either preserved or reduced ejection fraction (EF).
• At least one clinical sign of volume overload, such as:
• Pleural effusion (confirmed by chest X-ray or ultrasound).
• Oedema or ascites (verified by abdominal ultrasonography).
• Plasma NT-proBNP level > 1000 pg/mL or BNP level > 250 ng/mL at screening.
• Receiving at least 40 mg of furosemide as oral maintenance therapy for at least one month prior to the study initiation.

Exclusion Criteria:

• Previous use of acetazolamide or metolazone prior to the study period.
• Known hypersensitivity or allergies to the study drugs (acetazolamide or metolazone) or their components.
• Patients with electrolyte disturbances, especially hypokalemia.
• End-stage renal disease requiring dialysis or GFR < 20 mL/min/1.73 m².
• Pregnant or breastfeeding women.
• Severe hypotension (systolic blood pressure < 90 mmHg) or other significant comorbidities like congenital cardiac illness requiring surgery.
• Patients requiring renal replacement therapy during the hospitalization.
• History of significant electrolyte imbalances or acid-base disturbances.