Background: Cardiac surgery disrupts homeostasis, putting the patient in danger. Weaning from a ventilator requires clinical judgement and multiple signs. Patients recovering from anaesthesia can restart spontaneous ventilation. Cardiopulmonary bypass recovers during breathing. Weaning patients from mechanical ventilation after heart surgery involves vital capacity, tidal volume, respiratory rate, and minute ventilation. Others have related advanced age, comorbidities, protracted extracorporeal circulation, cardiac dysfunction, and low cardiac output to unsuccessful weaning of cardiac patients from mechanical ventilation and postoperative hemodynamics and neurological alterations to long-term ventilation. Aim: To determine predictors of unsuccessful weaning from mechanical ventilation after cardiac surgery, and therefore avoid the potentially hazardous long stay in ICU. Subjects and Methods: This study was conducted at Ain Shams University Hospital, post cardiac surgery ICU including 80 patients undergo cardiac surgery and receiving mechanical ventilation after operation.