EVEREST: Efficacy of Vasopressin Antagonism in hEart failuRE: Outcome Study With Tolvaptan

Inclusion Criteria: * Age greater than or equal to 18 years. * Current hospitalization for chronic congestive heart failure with admission up to 48 hours prior to randomization. Chronic heart failure is defined as requiring treatment for a minimum of 30 days prior to hospitalization. The subject must have signs of extracellular volume expansion, defined as two or more of the following: a) jugular venous distention; b) pitting edema (\>1+); or c) dyspnea. * NYHA Class III or IV at the time of hospitalization. * Left Ventricular Ejection Fraction \< = 40% within one year. Exclusion Criteria * Women who will not adhere to the reproductive precautions as outlined in the Informed Consent form. * Positive urine pregnancy test. * Inability to provide written informed consent. * Cardiac surgery within 60 days of potential study enrollment, excluding percutaneous coronary interventions. * Planned revascularization procedures, electrophysiologic (EP) device implantation, cardiac mechanical support implantation, cardiac transplantation, or other cardiac surgery within 30 days following study enrollment. * Subjects who are on cardiac mechanical support. * History of bi-ventricular pacer placement within the last 60 days. * Co-morbid condition with an expected survival less than six months. * Subjects with acute ST segment elevation myocardial infarction at the time of hospitalization. * History of sustained ventricular tachycardia or ventricular fibrillation within 30 days, unless in the presence of an automatic implantable cardioverter defibrillator. * History of a cerebrovascular accident within the last 30 days. * Hemodynamically significant uncorrected primary cardiac valvular disease. * Hypertrophic cardiomyopathy (obstructive or non-obstructive). * CHF due to uncorrected thyroid disease, active myocarditis or known amyloid cardiomyopathy. * Subjects with progressive or episodic neurological disease such as multiple sclerosis or history of multiple strokes. * History of primary significant liver disease or acute hepatic failure, as defined by the investigator. * History of poorly controlled diabetes mellitus. * Morbid obesity, defined as \> 159 kg (or 350 lbs) or BMI \> 40. * Supine systolic arterial blood pressure \< 90 mmHg. * Serum creatinine \> 3.5 mg/dL or \> 309.4 mmol/L. * Serum potassium \> 5.5 mEq/L or \> 5.5 mmol/L. * Hemoglobin \< 9 g/dL or \< 90 g/L. * History of hypersensitivity and/or idiosyncratic reaction to benzazepine derivatives (such as benazapril). * History of drug or medication abuse within the past year, or current alcohol abuse. * Inability to take oral medications. * Participation in another clinical drug or device trial within the past 30 days. * Previous participation in this or any other tolvaptan clinical trial.