Inclusion Criteria:  ORBITA CTO will enrol patients who meet all 5 of the following criteria:  Accepted for CTO PCI procedure by a specialist CTO operator.  Patients with symptoms related to a single vessel CTO (≥3 months duration, or probable CTO where duration is unknown) in a vessel of at least 2.5mm diameter without angiographically significant (LMS ≥50%, LAD/Cx/RCA/Graft ≥70%, ≥2mm diameter) coronary artery stenosis in remaining non-CTO vessels.  Symptoms are:  a) Typical exertional angina defined as: i) constricting discomfort in the front of the chest or in the neck, jaw, shoulder or arm ii) precipitated by physical exertion iii) relieved by rest or nitrates within 5 minutes b) Angina symptoms at rest (including decubitus angina and post-prandial angina).  c) Shortness of breath on exertion considered to be angina equivalent.  Clinical evidence of ischaemia in CTO territory on dobutamine stress echocardiography, nuclear myocardial perfusion scan, stress perfusion CMR or PET). Evidence of viability: If left ventricular angiogram or echocardiogram demonstrates LV impairment or RWMA then viability must be demonstrated. J-CTO score ≤ 3.  Exclusion Criteria:  Acute coronary syndrome within 4 weeks. PCI to non-CTO lesion in prior 4 weeks as part of ACS or elective PCI. Non-revascularised clinically important non-CTO vessel. Proven ischaemia (invasive or non-invasive) in non-culprit territory. Contraindications to PCI or drug-eluting stent (DES) implantation. Inability to tolerate or contraindication to DAPT. Severe valvular heart disease. Severe chronic pulmonary disease (FEV1 <30% of predicted value). Severe musculoskeletal disease resulting in immobility. Life expectancy <2years. Pregnancy. Age <18years. Inability to consent.