A 4-year-old boy with an atrial septal defect underwent minimally invasive repair via a small axillary incision. A bronchial blocker was used to occlude the right main bronchus, and one-lung ventilation was performed, which provided a better surgical field of view for the surgeons. Compared with adults, children, especially infants, have softer ribs and functional residual volume close to residual volume level, making them prone to hypoxemia during one-lung ventilation. In anesthetic management for such children, we should consider the pathophysiological changes caused by one-lung ventilation and the impact of left-right cardiac shunt.