Inclusion Criteria:  children under 6 years of age (range 4 days to 61 months) scheduled for surgery for congenital heart disease with chest computed tomography (CT) images including upper airways  Exclusion Criteria:  pediatric patients with intubation or tracheostomy before general anesthesia due to underlying disease small sized airway with inner diameter <3.0 mm because of pre-term or low birth weight unstable vital signs during induction history of difficult intubation emergency surgery where printing a 3D airway model in advance was not possible