Inclusion Criteria:  Participant is willing and able to give informed consent for participation in the study. Male or Female, aged 18 years or above. Been treated with percutaneous coronary intervention of either drug coated balloon or drug eluting stent  Exclusion Criteria:  Any contraindications to administration of acetylcholine or GTN History of coronary vasospasm or spontaneous coronary artery dissection Significant medical, surgical or psychiatric disease that would affect subject safety or influence the study outcome according to physician's opinion Patients who received a combination of drug eluting stents and drug coated balloon to the same vessel Significant renal impairment (estimated glomerular filtration rate <30mL/min/ 1.73m2 Body mass index >35 (may affect coronary artery diameter qualitative assessment) Symptomatic congestive cardiac failure Severe asthma Significant autoimmune inflammatory conditions (for example rheumatoid arthritis) Patients taking immunomodulating drugs (including Methotrexate, Ciclosporin, steroids) Previous heart transplant Relative Anaemia - Haemoglobin <12g/dL in men and <10g/dL in women Women of child bearing age with a positive pregnancy test