Problem
During a routine physical examination, a male patient is found to have mild lower extremity edema and a faint S3 heart sound. Laboratory assessment reveals the following:
Na+ 121 mEq/L
K+ 3.5 mEq/L
Cl- 89 mEq/L
CO2 25 mEq/L
BUN 19 mg/dL
Creatinine 1.0 mg/dL
Serum osmolality 244 mOsm/L.
What is the likely underlying abnormality in this patient?