Hyponatremia is a common electrolyte disorder with the potential to cause serious neurological complications. Conventional therapies for hyponatremia have been found to be inconsistently effective. Arginine vasopressin (AVP) is etiologically critical for hyponatremia, and it has been proven that AVP receptor (AVP-R) antagonists normalize serum sodium levels in hyponatremic patients. Additionally, one of these drugs showed potential for reducing mortality in patients with decompensated heart failure and for suppressing the progression of genetic renal disease in animals. The first non-peptide AVP-R antagonist has recently been approved in the United States. It is expected that this approval will accelerate the development of future clinical applications of AVP-R antagonists and open the door to a new era in the treatment of these intractable diseases.