Safety Study of Vasopressin V2 Receptor Antagonist on Patients With Severe Chronic Heart Failure (AQUAVIT).

Men or women with chronic heart failure (NYHA Class IIIB and IV).
Women must be post-menopausal or surgically sterilized; they cannot be pregnant or nursing.
Age 21 to 80 years.
Chronic heart failure of at least 3 months duration. For 2 months prior to screening, patients must have had symptoms at rest or on minimal exertion for more than 50% of the time. For 2 weeks prior to screening, patients must have had symptoms at rest or on minimal exertion for more than 90% of the time.
Patients must be receiving a diuretic and an ACE inhibitor (or an angiotensin II receptor antagonist) for the treatment of heart failure.
Patients may be receiving digoxin, a beta-blocker or spironolactone