Microvascular Coronary Rehabilitation For Improving Treatment - Feasibility Study

Inclusion Criteria: * Age ≥18 * Angina or angina equivalent symptoms * Unobstructed coronary arteries at the time of coronary angiogram. This will be defined as plaque causing \<40% epicardial vessel stenosis or 40-90% with a fractional flow reserve (FFR) ≥0.8 * Evidence of microvascular dysfunction on ICA (CFR \<2.5 and/or AchFR \<1.5) Exclusion Criteria: * New York Heart Association class III/IV heart failure * Severe left ventricular impairment (ejection fraction≤35%) * Severe heart valve disease * Significant cardiomyopathy (as assessed by a cardiologist) * Severe hypertension (defined as blood pressure \>180/120mmHg (despite three anti-hypertensive agents) * Uncontrolled arrhythmia * A history of aortic dissection, recent (\<6 months) acute pulmonary embolus, deep vein thrombosis, stroke or transient ischaemic attack, severe autonomic or peripheral neuropathy, acute systemic illness or fever, severe acute or chronic renal failure, severe pulmonary fibrosis or interstitial lung disease (in line with other trials investigating HIIT exercise) * Pregnancy or breastfeeding (at any point during the study. Patients becoming pregnant during the study will be asked to withdraw due to additional radiation exposure and risks from HIIT) * Physical inability to participate in exercise * Significant claustrophobia or metallic implants which would limit MRI imaging * Intolerance to regadenoson testing (high degree atrioventricular block, severe asthma or airways disease) * Current participation in another intervention-based trial * Inability to fully understand the verbal and written descriptions of the study and instructions provided during the study duration.