Vasoplegic syndrome after cardiac surgery is a common complication after cardiac surgery, with negative impact on patient outcomes and hospital costs. Pathogenesis of vasodilatory phenomenon after cardiac surgery remains a matter of controversy. Loss of vascular tone can be partly explained by the depletion of neurohypophyseal arginine vasopressin stores. The investigators hypothesized that the use of arginine vasopressin would be more effective on treatment of shock after cardiac surgery than norepinephrine, decreasing the composite end point of mortality and severe morbidity.

Inclusion Criteria:

• need vasopressor support

Exclusion Criteria:

• younger than 18 years;
• surgery without cardiopulmonary bypass;
• emergency procedure;
• ascending and descending thoracic aortic procedures;
• left ventricular aneurysm resection; enrollment in another study;
• pregnancy;
• neoplasm;
• Raynaud's phenomenon, systemic sclerosis or vasospastic diathesis;
• severe hyponatremia (Na<130mEq/L);
• acute mesenteric ischemia;
• acute myocardial infarction;
• cardiogenic shock; and refusal to consent