Samsca (generic name Tolvaptan) is used to treat low levels of salt (sodium) in the blood, which can be the result of conditions such as heart failure and an imbalance of certain hormones in the body. Tolvaptan belongs to a class of drugs known as vasopressin receptor antagonists that work by increasing urine production, causing the body to excrete more water. This helps to gradually increase the blood salt level and reach the normal value.