3. Persistent dilutional (euvolemic or hypervolemic) hyponatremia defined as being documented as present for at least 48 hours, evidenced by at least 2 serum sodium assessments < 130 mEq/L (mmol/L) drawn at least 12 hours apart (these values can be documented using historical values previously obtained per standard of care); a third (STAT) serum sodium assessment < 130 mEq/L (mmol/L), which will serve as the baseline value for efficacy endpoints, is to be obtained within 2 to 4 hours prior to the first dose of tolvaptan