Next to environmental risk factors, the investigators believe that there is an important role of genetic predisposition to develop PAH in CHD. 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 the genotype is 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.