Patients who have had stents in their coronary arteries (PCI) have to stay on antiplatelet agents to prevent clotting of their stents. These patients often require non-cardiac surgery (NCS) at some stage after their PCI. The rate of major cardiac complications (MACE)in this population is very high and it is unclear why they are at higher risk than the general population. It is possible their antiplatelet is not adequate, or that surgery causes them to be more clot prone. This is a prospective, multicentre observational study.