NPPB and hydrops fetalis: Two weeks later, the patient's HF status became stable and the serum BNP concentration returned to normal (55 pg/mL).<h4>Discussion</h4>The present case indicates that the classic diuretic of acetazolamide would have a vasopressin blockade-like effect and could be an alternative diuretic to vasopressin antagonists for some proportion of HF patients with hyponatraemia.