Abstract Aims Hyponatremia is associated with poorer outcomes and diuretic response in patients hospitalized for heart failure. This study compared a tolvaptan‐based vs. furosemide‐based diuretic regimen on short‐term clinical responses in hyponatremic acute heart failure. Methods and results Prospective, randomized, open‐label, parallel‐group, single‐centre study comparing oral tolvaptan vs. continuous infusion furosemide. Thirty‐three subjects requiring hospitalization for acute congestive heart failure, and a serum sodium