This is a 1:1 ratio single-center, double-blind, randomized controlled trial, aiming to enroll 130 patients admitted in infusion ward. The participants receive furosemide as standard treatment and will randomize towards 250 mg oral acetazolamide twice a day versus placebo on three consecutive days. The main objective is to determine the effect of oral acetazolamide and furosemide combination therapy on the decongestion. Prespecified secondary objectives included N-terminal pro B-type natriuretic peptide level on the 30th day, the readmission rate in a three-month period, quality of life assessment by Heart Failure Quality of Life Questionnaire at the end of the third month, change in weight, creatinine level, urinary sodium excretion, potassium level, and hematological indices in complete blood count at third day of the trial.

This is a 1:1 ratio single center, double-blind, RCT on the diuretic and decongestive effects of oral acetazolamide in Iranian patients with HF. This study will be conducted on heart failure patients whose symptoms of congestion are not relieved by oral diuretics and are temporarily hospitalized in a section called the infusion ward and receive intravenous diuretics. The infusion unit is a separate unit where patients with heart failure who are not adequately relieved by oral diuretics are admitted for a short period of time and receive injectable furosemide. In this study, 250 mg acetazolamide tablets and placebo and furosemide 20 mg will be used. The medical information of the patients will be recorded, patients' clinical status will be evaluated by calculating the EVEREST score at baseline and third day , the weight and laboratory indices will also be measured at baseline and third day based on the same scale and fixed laboratory kits, respectively. Blood pressure will be also measured by an expert nurse at the baseline and each day before the furosemide injection by the same blood pressure cuff. Patients will be followed for clinical events to day 90. The protocol was drafted according to the standard protocol items for clinical trials) SPIRIT) guideline for randomized clinical trial protocols.

Study objectives The main objective is to determine the effect of oral acetazolamide and furosemide, as a loop diuretic, combination therapy on improvement of the congestion in patients at baseline and third day. Urinary sodium to creatinine ratio is an indicator in this objective and will be measured at 2 P.M. in these days.

Prespecified secondary objectives included the following: N-terminal pro B-type natriuretic peptide (NT-proBNP) level on the 30th day, the hospitalization rate in a three-month period, comparison of quality of life between two groups at the end of the third month and change in weight, creatinine level, urinary sodium excretion, potassium level, and hematological indices in complete blood count (CBC) at third day of the trial. At the end of the third month, we will assess our patients' quality of life using the Iranian Heart Failure Quality of Life (IHFQoL) Questionnaire. The validity and reliability of this questionnaire, which has 16 questions in 5 dimentions, has been confirmed by Naderi et al in 2012. (Kornbach's alpha coefficient= 0.922) .This questionnaire offers a range of total scores between 20 and 66. The items are scored on a three- or four-point Likert scale, with a higher score indicating a better quality of life for the individual. These are the five dimensions that are the subject of this survey: severity of disease symptoms (items 1, 2, 3, 4, 6), physical limitations (items 7-1 to 7-6), mental limitations (items 5, 9, 11), social aspects (items 8, 10, 12, 13), self-care (items 14, 15) and the patient's overall satisfaction (item 16). (16)

Inclusion criteria

1. Earn at least 8 points from EVEREST score (see Table 1.)
2. Adult patients (≥ 18 years)
3. A major clinical sign of volume overload including edema, ascites confirmed by abdominal ultrasound, or pleural effusion confirmed by chest x-ray or chest ultrasound without using iv furosemide.
4. Maintenance treatment with oral furosemide as a loop diuretic ≥20 mg for at least one month
5. Using SGLT2i drugs including canagliflozin, dapagliflozin, and empagliflozin for at least one month

Exclusion criteria

1. Systolic blood pressure less than 90 mmHg or mean arterial pressure less than 65 mmHg
2. Estimated glomerular filtration rate (eGFR) <20 ml/min/1.73 m2
3. Using any diuretic agent except mineralocorticoid receptor antagonists including spironolactone and eplerenone
4. Simultaneous diagnosis of acute coronary syndrome, which is characterized by typical chest pain in addition to an increase in troponin level above the 99th percentile or electrocardiographic changes indicating ischemia or hospitalization as unstable angina.