Learning by Heart: The Effectiveness of an EF Training Program for Pre-schoolers With a Severe CHD

In order to be eligible to participate in this study, a child must meet all of the following criteria: * Aged 4.0 - 6.0 years upon inclusion OR aged 6.0-7.0 years who are still in kindergarten (group 1 \& 2 of the Dutch school system) * Required CHD surgery in the first six months of life (with or without ECMO) or a cyanotic CHD that required surgery in the first 12 months of life * IQ estimated \> 55 (no moderate to severe intellectual disability) * Diminished EF based on a below average score on any of the subtests of the 'KleuterExtra' test battery (≤ 25 percentile) at t = 0 * Sufficient comprehension of the Dutch language by the child to be able to participate in the EF test battery and the EF training program. In order to be eligible to participate in this study, the parent(s) must meet the following criteria: * Sufficient comprehension of the Dutch language to understand the study information and to be able to fill out the Dutch questionnaires. Exclusion Criteria: * Children receiving targeted EF support at school upon inclusion. * Children with severe brain damage (estimated IQ \< 55) * Genetic syndromes known to directly affect cognitive performance (e.g. Down syndrome) * Children with severe psychiatric disorders upon inclusion that require treatment first, such as a posttraumatic stress disorder, separation anxiety disorder, or reactive attachment disorder.