 Hyponatremia is defined as a serum sodium concentration below the lower limit of normal and is the most frequently encountered electrolyte abnormality in hospitalized patients. Generally speaking, most cases of hyponatremia are mild. However, as the serum sodium falls below 130 mEqL, the possibility of significant morbidity and mortality increases, and most clinicians will initiate corrective therapy for serum sodium values approaching 130 mEqL and lower. The reasons for treating hyponatremia relate both to the symptoms, which may be quite disturbing to patients, as well as to potential outcomes including permanent neurological damage and death. there is also growing awareness of the association between hyponatremia and increased mortality in patients with heart failure. 