Sponsor decided to quit funding before any enrollments

Patients being hospitalized for acute heart failure and already receiving standard therapy will be randomized to receive either tolvaptan or placebo, based on the level of copeptin measured in their bloodstream. Patients with high copeptin levels will be able to participate in the trial, patients with low levels will be excluded. Patients being admitted to the observation unit for acute heart failure and already receiving standard therapy will be randomized to receive either tolvaptan or placebo without consideration of the copeptin level. The hypothesis is that patients receiving tolvaptan will have better improvement of shortness of breath than those receiving placebo, within 9 hours of drug administration.

Inclusion Criteria:

1. Older than or equal to 18 years of age, with diagnosis and planned treatment for Acute Heart Failure
2. Dyspnea at rest or minimal exertion per the patient
3. Evidence of extracellular volume expansion by at least one of the following: JVD, Rales, Ascites, Edema or positive Chest X-ray defined as cardiomegaly, pulmonary vascular congestion, Kerley B-lines, pulmonary edema and/or pleural effusion.
4. Elevated BNP level >200 pg/ml, or NTproBNP > 1000pg/mL
5. Able to administer study drug within 8 hours from triage time

Inpatient Hospitalized Inclusion Only:

Co-peptin level > 27 pmol/L

Exclusion Criteria:

1. Unable to provide informed consent
2. Unable to have 30 day telephone follow up
3. Not expected to survive past 6 months
4. On Renal replacement therapy or creatinine >3.5
5. History of allergy or intolerance to Tolvaptan
6. Suspected Pregnancy
7. Cardiogenic Shock
8. Participation in any interventional trial in prior 30 days.
9. Receiving or planned to receive IV Inotropic therapy
10. ACS now or in the past 30 days
11. Treatment with IV infusion vasoactive drugs in the hour prior to enrollment
12. Temperature > 100.5
13. Heart Failure due to atrial fibrillation with Rapid Ventricular Response
14. SBP < 90 mmHg