The project is designed as a long-term follow-up and method study. A cohort of 20 children who in the 1990's underwent surgical closure of a congenital VSD will be asked to participate in this study. An equal amount of healthy young adults, will function as control group. Each participant will complete two different exercise tests, a MRI of the heart during lower body exercise on a supine ergometer bicycle, and a Supine ergometer bicycle exercise test. This data can be used for comparing cardiac output between the test groups, and furthermore it allows an evaluation of the correlation between the two methods.