1. From the University of Oxford Centre for Clinical Magnetic Resonance Research (J.B.S., S.E.P., J.M.F., A.K., F.W., S.N.), and the Departments of Cardiovascular Medicine (J.B.S., S.E.P., J.M.F., A.K., F.W., S.N.) and Cardiothoracic Surgery (D.P.T.), University of Oxford, John Radcliffe Hospital, Oxford, UK.