Inclusion Criteria:

• Male or female patient ≥21 years old
• Admitted to hospital for AHF with at least 1 symptom (dyspnea, orthopnea, or fatigue) and 1 sign (rales on auscultation, peripheral edema, ascites, pulmonary vascular congestion on chest radiography) of congestion
• Patient must be randomized within 24 hours of first IV diuretic dose administered for the current episode of decompensation (regardless of where the diuretic was given e.g. office, ED, ambulance, hospital etc.)
• Estimated GFR of ≥30 mL/min/1.73m2 determined by the MDRD equation
• Serum K+ ≤5.0 mmol/L at enrollment
• NT-proBNP ≥1000 pg/mL or BNP ≥250 pg/mL, measured within 24h from randomization
• Not on MRA or on low-dose spironolactone (12.5 mg or 25 mg daily) at baseline

Exclusion Criteria:

• Taking eplerenone or >25 mg spironolactone at baseline
• eGFR < 30 ml/min/1.73m2
• Serum K+ >5.0 mmol/L. If a repeat measurement within the enrollment window is <5.0, the patient can be considered for inclusion.
• Systolic blood pressure <90 mmHg
• Hemodynamically significant arrhythmias or defibrillator shock within 1 week
• Acute coronary syndrome currently suspected or within the past 4 weeks
• Severe liver disease (ALT or AST >3 x normal, alkaline phosphatase or bilirubin >2x normal)
• Active infection (current use of oral or IV antimicrobial agents)
• Active gastrointestinal bleeding
• Active malignancy other than non-melanoma skin cancers
• Current or planned mechanical circulatory support within 30 days
• Post cardiac transplant or listed for transplant and expected to receive one within 30 days
• Current inotrope use
• Complex congenital heart disease
• Primary hypertrophic cardiomyopathy, infiltrative cardiomyopathy, acute myocarditis, constrictive pericarditis or tamponade
• Previous adverse reaction to MRAs
• Enrollment in another randomized clinical trial during index hospitalization