Tolvaptan is an oral medication used to treat low blood sodium levels (hyponatremia) associated with conditions such as heart failure or SIADH (syndrome of inappropriate antidiuretic hormone). It works by blocking the effects of vasopressin, a hormone that causes the body to retain water, thus helping to restore the natural balance of fluids. Samsca promotes the excretion of free water without significant loss of sodium or potassium, making it distinct from traditional diuretics.