1. From the Cardiovascular Magnetic Resonance Unit (W.M.B., R.A., P.J.K., R.H.M.) and Department of Pathology (M.N.S.), Royal Brompton Hospital; Pulmonary Hypertension Service (J.S.R.G.), Hammersmith Hospital; and the National Heart and Lung Institute (W.M.B., P.J.K., J.S.R.G., M.N.S., R.H.M.) Imperial College, London, England.