Aim: Cardiac malformations resulting in cyanosis, such as transposition of the great arteries (TGA), have been associated with neurodevelopmental dysfunction. The purpose of this study was to assess, for the first time, theory of mind (ToM), which is a key component of social cognition and executive functions in school-aged children with TGA. Method: Twenty-one children (14 males, seven females; mean age 7y 4mo; SD 3mo) who underwent neonatal open-heart surgery for TGA using full-flow cardiopulmonary bypass were compared with 21 typically developing age-matched children (12 males, nine females; mean age 7y 6mo; SD 3.8mo) using different neuropsychological measures specifically designed to assess executive function (cognitive and response inhibition, verbal and spatial working memory, and planning). They were also given two ToM tasks (first- and second-order false belief understanding). Results: General IQ was within the normal range in both the TGA group and the comparison group (mean IQ 113 [SD 9.3] and 118 [SD 10.1] respectively), but performance on all executive functions and on ToM (first and second level) was significantly lower in the TGA group (p values of 0.02, 0.01, and 0.004 respectively). A discriminant multivariate analysis provided evidence for cognitive and behavioural inhibition as well as performance on false belief tasks as being the most important contributors to the differentiation between the groups (p = 0.03). Interpretation: Children with TGA demonstrate great difficulties in exerting cognitive and behavioural inhibition. They also present specific deficits in false belief understanding, which were related to immature executive abilities.