Introduction and objectiveCongenital heart disease (CHD) is a complex condition requiring a multidisciplinary approach. It is crucial that adults with CHD (CHD) have adequate knowledge of their condition, enabling them to engage in their healthcare decisions and self-management. We aimed to investigate knowledge and perception among adults of their CHD. MethodsSingle-center, observational, cross-sectional study. A 25-item adapted survey of Leuven Questionnaire for CHD was used to assess four main domains: (1) disease and treatment, (2) endocarditis and preventive measures, (3) physical activity and (4) reproductive issues. ResultsOne hundred forty-eight patients participated in the study. Patients had a significant lack of knowledge localizing their heart defect, recognizing drug side effects, acting in case of experiencing drug side effects, recognizing at least two symptoms of clinical deterioration, to adequately define endocarditis and most typical signs and risk factors, to acknowledge the hereditary nature of their CHD and risk of clinical deterioration during pregnancies. Patients with an education level ≥12th grade have higher knowledge in various items and, overall, the complexity of CHD was not associated with a better performance. ConclusionThis study highlights the existing knowledge gaps among adults with CHD. It underscores the need for tailored information and structured educational programs to improve management. By addressing these challenges, healthcare providers can enhance patient outcomes, improve quality of life, and promote long-term well-being for individuals with CHD.