 The second part of this study will focus on understanding disease mechanisms utilising MR imaging techniques and using the Sheffield PH Biobank resource to understand differences in the IPAH and distal CTEPH cohorts. The Sheffield PH Biobank has samples and detailed phenotypic data on over 400 treatment naïve patients with all forms of pulmonary hypertension with serial sampling and long term follow up providing a unique resource to make detailed comparisons across all forms of pulmonary hypertension. 