"SALT Trial" Study of Ascending Levels of Tolvaptan in Hyponatremia

Inclusion Criteria * Hyponatremia in euvolemic or hypervolemic states, defined as serum sodium \<135 mEq/L prior to randomization * Able to give Informed Consent. Exclusion Criteria * Women who are breast feeding and females of childbearing potential who are not using acceptable contraceptive methods * Hyponatremia in hypovolemic states * Acute and transient hyponatremia associated with head trauma or post-operative state * Hyponatremia due to uncontrolled hypothyroidism or uncontrolled adrenal insufficiency * Cardiac surgery within 30 days of potential study enrollment, excluding percutaneous coronary interventions * History of a myocardial infarction within 30 days of potential study enrollment * History of sustained ventricular tachycardia or ventricular fibrillation within 30 days, unless in the presence of an automatic implantable cardioverter defibrillator * Severe angina including angina at rest or at slight exertion and/or unstable angina * History of a cerebrovascular accident within the last 30 days * Subjects with psychogenic polydipsia may not be included, however subjects with other psychiatric illness may be included * Systolic arterial blood pressure \< 90 mmHg * History of hypersensitivity and/or idiosyncratic reaction to benzazepine or benzazepine derivatives (such as benazepril) * History of drug or medication abuse within the past year,or current alcohol abuse * Uncontrolled diabetes mellitus defined as fasting glucose \> 300 mg/dL * Urinary tract obstruction except benign prostatic hyperplasia (BPH) if non-obstructive * Previous participation in another clinical drug trial within the past 30 days * Previous participation in this or any other tolvaptan clinical trial * Terminally ill or moribund condition with little chance of short term survival * Serum creatinine \> 3.5 mg/dL * Serum sodium \< 120 mEq/L with associated neurologic impairment, i.e. symptoms such as apathy, confusion, seizures * Patients with progressive or episodic neurologic disease such as multiple sclerosis or history of multiple strokes * Child-Pugh score greater than 10 (unless approved) * Patients receiving intravenous fluids at a rate greater than KVO (Keep Vein Open) * Hyponatremia due to lab artifacts * Patients receiving arginine vasopressin (AVP) or its analogs for treatment of any condition * Patients receiving within 7 days of randomization, other medications for treatment of hyponatremia specifically: demeclocycline, lithium carbonate or urea * Patients likely requiring intravenous (IV) saline for correction of symptomatic or asymptomatic severe hyponatremia during the course of the study * Severe pulmonary artery hypertension * Hyponatremia should not be the result of any medication that can safely be withdrawn.