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 i…