Inclusion Criteria:  Adults over 18 years of age Patients who underwent one lung ventilation using a bronchial blocker for minimally invasive cardiac surgery If there is no atelectasis on chest X-ray or chest computed tomography performed before surgery  Exclusion Criteria:  If there is evidence of atelectasis, pneumonia, or lung disease that can reduce lung volume in a chest X-ray examination or chest computed tomography performed before surgery Patients scheduled for sternotomy If there is a skin disease in the chest that requires EIT measurement If there is a plan to transfer to the intensive care unit while maintaining the endotracheal tube