Objective To determine the effects of different ventilation level on cerebral blood flow after bidirectional superior cavopulmonary anastomosis. Methods Eight pediatric patients who underwent bidirectional superior cavopulmonary amastomosis were enrolled in this study. Patients were studied within 3-5 hours after the operation while stable hemodymic status achieved. Initial ven-tilation parameters were set as synchronized intemittent mandatory ventilation, volume control mode. Different veafilafion level was achieved by adjusting mechanical ventilation frequency. Blood gas analysis, hemodynamic parameters and Doppler determinations of internal carotid artery were obtained after at least a 20-minute stabilization period at each time point of the protocol. During the study the oxyhemoglobin in the cerebral tissue was continually monitored using near-infrared spectroscopy. Results During hyperventila-tion, there were significant decreases in arterial pressure and superior vena cava pressure. The mean arterial partial pressure of oxygen and carbon dioxide both decreased significantly,while the peak velocity d the internal carotid artery blood flow and the oxyhemoglobin in the cerebral tissue which represent the profusion d the cerebral tissue was also decreased significantly. During hypoventilation, the opposite phenomenon were observed. Conclusion Hemodyamic status, systemic oxygenation, cerebral blood flow and thus the pul-monary blood flow can be affected by ventilation level after bidirectional superior cavapulmonary anastomosis. Compared with hyperven-tilation, hypoventilation improves systemic oxygenation and arterial blood pressure. The mechanism of these effects is supposed that hy-poventilation decreases cerebral vascular resistance, thus increasing blood flow through cerebral-pulmonary series after superior bidirec-tional cavapulmonary anastomosis.