Abstract Background The oral vasopressin-2 receptor antagonist tolvaptan causes aquaresis in patients with volume overload, potentially facilitating decongestion and improving the clinical course of patients with acute heart failure (AHF). Objectives To address the acute use of tolvaptan to improve congestion in AHF, we conducted the Targeting Acute Congestion with Tolvaptan in Congestive Heart Failure (TACTICS-HF, NCT01644331) study. Methods TACTICS-HF randomized patients within 24 hours of AHF presentation in a prospective, double blind, placebo-controlled trial. Patients were eligible regardless of ejection fraction, and were randomized to either 30 mg of tolvaptan or placebo given at 0, 24, and 48 hours, with a fixed-dose furosemide regimen as background therapy. The primary endpoint was the proportion of patients considered responders at 24 hours. Secondary endpoints included symptom improvement, changes in renal function, and clinical events. Results A total of 257 patients were randomized. Dyspnea relief by Likert scale was similar between tolvaptan and placebo at 8 hours (25% moderately or markedly improved for tolvaptan vs. 28% placebo, p=0.59) and at 24 hours (50% tolvaptan vs. 47% placebo, p=0.80). Need for rescue therapy was also similar at 24 hours (21% tolvaptan, 18% placebo, p=0.57). The proportion defined as responders at 24 hours (primary study endpoint) was 16% for tolvaptan and 20% for placebo (p=0.32). Tolvaptan resulted in greater weight loss and net fluid loss compared to placebo, but tolvaptan-treated patients were more likely to experience worsening renal function during treatment. There were no differences in in-hospital or post-discharge clinical outcomes. Conclusions In patients hospitalized with AHF, dyspnea, and congestion, the addition of tolvaptan to a standardized furosemide regimen did not improve the number of responders at 24 hours despite greater weight loss and fluid loss.