Inclusion Criteria:  Provision of informed consent prior to any study specific procedures Male or female aged greater than 18 years  Existing diagnosis of a chronic coronary syndrome:  (i) History of stable angina or (ii) History of an acute coronary syndrome event >1 year ago or (iii) Previous evidence on imaging of either at least one stenosis >50% in an epicardial coronary artery or a myocardial perfusion defect  Receiving single antiplatelet therapy with aspirin 75 mg once daily  Exclusion Criteria:  Any history of haemorrhagic stroke or lacunar stroke History of ischaemic stroke or transient ischaemic attack in the last year Heart failure associated with NYHA class III or IV symptoms Estimated glomerular filtration rate <15 ml/min Planned procedure for coronary revascularization Any planned surgery or other procedure that may require suspension or discontinuation of antiplatelet therapy expected to occur within 3 months of randomisation Prior intention by patient or physician to discontinue aspirin within the study period Receiving doses of aspirin other than 75 mg once daily Treatment or planned treatment with antiplatelet medication apart from aspirin (eg. clopidogrel, prasugrel, ticagrelor, dipyridamole, ticlopidine) Current use of a loop, thiazide or potassium sparing diuretic (affects prostanoid assays) Any acute coronary syndrome event, percutaneous coronary intervention or coronary artery bypass grafting within 1 year prior to randomisation Current or planned use of an oral anticoagulant (e.g. warfarin, dabigatran, rivaroxaban [including 2.5 mg BD], apixaban, edoxaban) or parenteral anticoagulant (eg. unfractionated heparin, low molecular weight heparin, bivalirudin) Current or planned use of a GPIIb/IIIa inhibitor (eg. abciximab, tirofiban) Current or planned use of a fibrinolytic agent (eg. tissue plasminogen activator) Requiring or likely to require treatment with a non-steroidal anti-inflammatory drug (NSAID), including COX2 inhibitors, and including regular or intermittent/as required use Current or planned use of a strong CYP3A4 inhibitor (eg, ketoconazole, itraconazole, voriconazole, telithromycin, clarithromycin [but not erythromycin or azithromycin], nefazadone, ritonavir, saquinavir, nelfinavir, indinavir, atanazavir, cobicistat or over 1 litre daily of grapefruit juice), strong inducer (e.g. rifampin/rifampicin, rifabutin, phenytoin, carbamazepine, phenobarbital), a selective serotonin reuptake inhibitor (SSRI) or selective noradrenergic reuptake inhibitor (SNRI). Clinically significant liver disease, defined as known or suspected diagnosis of hepatic cirrhosis with current Child Pugh class B or C; or elevation of serum alanine transferase or aspartate transferase greater than 3 times the upper limit of the normal range for the processing laboratory. History of alcohol or drug abuse, defined as regular use of an illicit substance for recreational purposes or regular consumption of greater than 50 units (males) or 35 units (females) of alcohol per week, in the last year Co-morbidity associated with life expectancy less than 1 year Any other condition deemed by the investigator to significantly affect haemostasis, coagulation, bleeding risk or ability to comply with the study protocol. Females of child-bearing potential unless negative pregnancy test at screening and willing to use effective contraception (i.e. established use of oral, injected or implanted hormonal methods of contraception or placement of an intrauterine device (IUD) or intrauterine system (IUS) or barrier methods of contraception with spermicide or sole male partner with prior vasectomy and confirmed absence of sperm in ejaculate) for the duration of treatment with study medication.