MYKKE is a long-term prospective registry providing a core platform for clinical research studies, which can be attached in a modular fashion. After a six-month pilot phase including 8 centers, the basic registry was opened in June 2014 to all hospitals in Germany treating patients with paediatric heart disease. While the scientific lead is with two study coordinators and a study group consisting of principal investigators from the collaborating centres ("MYKKE Investigators"), MYKKE is hosted and technically administered by the Competence Network for Congenital Heart Defects, which was initiated in 2003 by the Federal Ministry of Education and Research of the German government and is now part of the German Center for Cardiovascular Research (DZHK). Ethical approval was first obtained at the initiating centre (Deutsches Herzzentrum Berlin) and subsequently confirmed by local authorities of all collaborating centres.