This Post-Marketing Surveillance will be conducted in accordance with the local regulation of New Drug Re-examination. The surveillance will be conducted for 6 years of the re-examination period (01Sep2011~31Aug2017). Each subject will be observed at least for 4 days during the surveillance period.

This study will be conducted as a prospective, single-arm, multicenter study. Findings on examination, diagnosis, opinions and observations implemented as per general medical practice during the observational period will be documented in the case report forms by the investigators or responsible staffs at the institution since the surveillance is an observational study.

Inclusion Criteria:

• Subjects must meet all of the following inclusion criteria to be eligible for enrollment into the study :

  1. Patients who have hyponatremia in euvolemic or hypervolemic states, defined as serum sodium level < 125 mEq/L or hyponatremia that is symptomatic and has resisted correction with fluid restriction
  2. Patients who are prescribed Samsca® treatment as per investigator's medical judgment
  3. Patients who gave written authorization to use their personal and health data
  4. Patients starting Samsca® treatment after agreement is in place Investigators will refer to the product market authorization (label) for inclusion criteria.

Exclusion Criteria:

• Subjects presenting with any of the following will not be included in the study:

  1. Patients who have been treated with Samsca®
  2. Patients with known or suspected hypersensitivity to tolvaptan or to any ingredient of the drug
  3. Patients requiring urgent intervention to raise serum sodium acutely.
  4. Inability of the patient to sense or appropriately respond to thirst.
  5. Hypovolemic hyponatremia
  6. Concomitant use of strong CYP3A inhibitors
  7. Anuric patients
  8. Volume depletion patients
  9. Hypernatremia patients
  10. Women who are pregnant or possibly pregnant and lactation
  11. Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption Investigators will refer to the product market authorization (label) for exclusion criteria.

The treatment of clinically significant hypervolemic and euvolemic hyponatremia [serum sodium < 125 mEq/L or hyponatremia that is symptomatic and has resisted correction with fluid restriction], including patients with heart failure, cirrhosis, Syndrome of Inappropriate Antidiuretic Hormone (SIADH) and etc.

all patients who received Samsca® tablets at least once and had at least one post-treatment assessment during the study in approved indication and dosage regimen

up to 4 days.