Inclusion Criteria:  Adults: age≥18 years. Typical HF symptoms (NYHA stage>I) within the last six months. Raised NTproBNP (>400 pg/ml) EF>50 % with the absence of structural heart disease on TTE (except left ventricular hypertrophy or left atrial enlargement).  Exclusion Criteria:  Patients unable/unwilling to provide informed consent. Bodyweight>120 kg or inability to lie flat/still. Contraindication for invasive workup (allergy to contrast, severe renal insufficiency with estimated glomerular filtration rate (eGRF)<30 ml/min). Contraindications for a contrast-enhanced CMR study (allergy to contrast, incompatible devices or implants, severe claustrophobia). Previous medical history of EF <50% Pregnancy  The extended observational arm of the study will have wider eligibility criteria  - Patients undergoing cardiac MRI for clinical indications irrespective of EF