1. From the Adult Congenital Heart Unit, Royal Brompton Hospital (S.V.B., O.G., C.S.B., G.A.P., M.A.G.); Centre for Advanced Magnetic Resonance in Cardiology, Royal Brompton Hospital (S.V.B., J.C.M., D.J.P., P.J.K.); and National Heart and Lung Institute, Imperial College (S.V.B., D.J.P., M.A.G., P.J.K.), London, UK.