We report a 62-year-old obese hypertensive Caucasian male patient with advanced COPD, pulmonary hypertension and acutely decompensating diastolic heart failure who presented with severe symptomatic life-threatening hyponatremia. Hypertonic 3% saline infusion did not improve hyponatremia even at 40 cc/h infusion rate and the patient was quickly experiencing worsening pulmonary edema with respiratory distress and imminent need for ventilatory support. The swift use of intravenous conivaptan, a vasopressin antagonist, with close 4-hourly monitoring of the serum sodium levels resulted in a prompt aquaresis with resolution of symptoms of pulmonary edema, fluid retention and simultaneous correction of life-threatening symptomatic hyponatremia. Vasopressin antagonists can be a life-saving therapeutic option in such critical clinical circumstances.