Urinary Chloride and Sodium Changes and Residual Congestion in Acute Heart Failure

The goal of this observational study is to learn how changes in urinary sodium and chloride levels relate to fluid overload and short-term outcomes in patients hospitalized with acute heart failure (AHF). The main questions it aims to answer are: * Do changes over time in urinary sodium and chloride reflect how well excess fluid is being removed during hospitalization? * Are these changes associated with residual congestion at discharge and with the risk of worsening heart failure or death after discharge? Participants hospitalized for AHF and treated with intravenous diuretics as part of their usual care will have clinical assessments, blood and urine tests, and echocardiographic evaluations collected at several time points during their hospital stay. Researchers will also record clinical outcomes, including worsening heart failure or death, at 30 days and 3 months after discharge.

Inclusion Criteria: * Provision of written informed consent prior to any study-related procedures; * Age ≥ 18 years; * Episode of AHF requiring hospital admission and treatment with intravenous furosemide; * New York Heart Association (NYHA) functional class II-IV; * NT-proBNP \>1000 pg/mL or BNP \>250 pg/mL, measured within a period not exceeding 24 hours prior to inclusion; * Transthoracic echocardiogram performed within the previous 24 months. All LVEF categories will be included: reduced LVEF (\