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Tolvaptan is widely used as an adjunct oral diuretic to loop and thiazide diuretics for the management of fluid overload in patients with congestive heart failure. Recently, tolvaptan sodium phosphate (TSP), a water-soluble prodrug of tolvaptan, was developed for intravenous administration and has demonstrated efficacy and safety in clinical settings. However, cases of TSP ineffectiveness have not yet been reported. Because oral tolvaptan does not work in some patients, TSP may also be ineffective in certain cases. We report the case of a 74-year-old male patient with chronic heart failure and chronic kidney disease who was unresponsive to TSP. The patient underwent off-pump coronary artery bypass grafting. Initially, intravenous furosemide and oral tolvaptan were administered to manage residual fluid overload; however, intravenous furosemide was discontinued owing to a decline in serum potassium levels. Oral loop and thiazide diuretics in combination with TSP were then added to ongoing oral tolvaptan therapy, but this regimen did not achieve sufficient weight reduction. Subsequently, high-dose intravenous furosemide was reintroduced in place of oral loop diuretics, with careful monitoring for hypokalaemia. Although high-dose intravenous furosemide worsened renal dysfunction, it successfully improved fluid overload and reduced plasma B-type natriuretic peptide levels, effects that persisted even after discontinuation of TSP. This case suggests that in patients with chronic kidney disease who are unresponsive to TSP, high-dose intravenous furosemide may provide more effective management of fluid retention in heart failure, though renal function must be closely monitored.