Vasopressin is a hormone from posterior pituitary. It is an octapeptide referred often as arginine vasopressin and antidiuretic hormone. It is emerging as an important advance in the treatment of variety of shock states. The current interest is for the use of ventricular fibrillation, sepsis and cardio pulmonary bypass. The pressor actions are complex and not understood completely. It has unique action in reversing some of the pathophysiological vasodilatation processes that occur in advanced shock, which are refractory to catecholamine vasopressors. Vasopressin 40 IU in refractory ventricular fibrillation is noted as level 2B evidence. Though well-known drug for many years, it has found many new indications.