1. From the Cardiovascular Magnetic Resonance Unit, Royal Brompton Hospital (C.B.-D., K.S., S.K.P.), Imperial College, National Heart and Lung Institute (C.B.-D., S.K., S.K.P.), Nuclear Medicine Department, Royal Brompton Hospital (E.R.), Cardiology Department, Chelsea and Westminster Hospital (F.S.N., E.R., S.K.), and Catheterization Laboratory, Royal Brompton Hospital (C.S.), London, United Kingdom.