Next to environmental risk factors, the investigators believe that there is an important role of genetic predisposition to develop PAH in CHD. In the past, certain genes have been identified that play a role in the development of atrial septal defect (ASD). There are also a lot of genes identified that play a role in PAH. Until now, not many research groups have studied a genetic link between CHD and PAH development. But it becomes more and more clear that there often is a discrepancy between the severity of PAH and the CHD, where it is useful to screen for PAH gene mutations. The investigators hypothesize that mutations in some of these known PAH genes or in other, still unidentified, genes are partly responsible for the phenotypic variability in patients with congenital shunt lesions, where some develop PAH and others do not. If a genetic predisposition for PAH in CHD could be identified, then genetic screening could be a useful additional tool for early detection of patients at risk of pulmonary vascular disease and PAH development, with new opportunities for prevention or early treatment.