Fibrosis; Heart

In this research study the investigators want to learn more about how well the investigators can visualize scar tissue in the heart by MRI. In patients with congenital heart disease who need a procedure in the electrophysiology laboratory, how the MRI findings match the findings in the electrophysiology laboratory is not known. This study works to answer these questions. Participants will undergo a cardiac MRI as part of the routine clinical care that was ordered by their doctors and additional imaging by cardiac MRI will be performed.