Patients admitted to the hospital due to acute decompensation of heart failure (ADHF) may manifest some deterioration in their renal function. The latter is associated with unfavorable outcomes: prolonged hospitalization and death. Cardiorenal syndrome type 1 (CRS1) is defined as a deterioration in renal function manifested by an increase in serum creatinine level by >0.3 mg% compared to patient's baseline level. The etiology of CRS1 is not clear and may be related to body fluid overload congesting the kidneys or dehydration reducing perfusion to the kidneys. Body fluid status is affected by diuretics. Presently, the practitioner has no objective data to assess whether CRS1 resulted from fluid overload or dehydration.