The research aims of this study are:
1. To further explore differences in a modified selection of patient-reported outcome measures (PROMs) and (as a new addition in APPROACH-IS II) explore differences in patient-reported experience measures (PREMs), by enrolling adults with congenital heart diseases in low, middle, and high income countries and including new potential explanatory variables ("Part 1").
2. To explore the profile and healthcare needs of a subgroup of older adults with congenital heart disease, with a particular focus on investigating the frailty phenotype ("Part 2").
