DEtection of Cellular Inflammation With FERumoxytol in the HEART

Inclusion Criteria: 1. One of the four conditions below: * Patients having undergone cardiac transplant * Patients diagnosed clinically with myocarditis of any aetiology (eg viral, septic, post chemotherapeutic etc) * Patients clinically diagnosed with cardiac sarcoidosis * Healthy volunteers 2. Age \> 18 years. Exclusion Criteria: 1. Contraindication to magnetic resonance imaging scanning identified from magnetic resonance imaging safety questionnaire 2. Patients refusing or unable to give informed consent 3. Renal failure (estimated glomerular filtration rate \<30 mL/min) 4. Polycythemia 5. Contraindication to ferumoxytol (previous allergic drug reaction, any immune or inflammatory conditions (eg, systemic lupus erythematosus, rheumatoid arthritis, history of severe asthma, eczema or other atopic allergy)), evidence of known iron overload, hemochromatosis, known hypersensitivity to ferumoxytol or its components or anaemia not caused by iron deficiency. 6. Known allergy to dextran- or iron-containing compounds. 7. Diagnosis of myocardial infarction within 1 month. 8. Pregnancy or Breast-feeding. 9. Women of child bearing age not ensuring reliable methods of contraception. Female participants of child bearing age will be asked if they are ensuring reliable methods of contraception prior to each administration of USPIO and MRI scan. If use of reliable contraception cannot be confirmed, the participant will be withdrawn.