The purpose of this Clinical Investigation is to use the PlaqueTec Liquid Biopsy System (LBS) to determine which biomarkers detected locally within the coronary artery can give information on the state of atherosclerotic disease. The LBS is a novel CE-marked class III coronary catheter designed for sampling blood directly from the coronary arteries. The LBS is unique in that it can capture "gradients" of biological molecules within the coronary artery and by analysing the samples it collects it can unequivocally identify which biomarkers have been locally released within the coronary artery. The samples can then be analysed for a variety of biomarkers using standard analytical techniques. Cardiologists should find this of great benefit as recent studies have shown that coronary artery disease is controlled and directed by the release of specific biological molecules into the blood from diseased areas of the coronary arteries. The safety and performance of the LBS has been proved previously in a recent First In Man study. The Clinical Investigation study will enroll 70 patients and will be observational in nature. The study is designed to use the device in its intended application (i.e. as an adjunct to a PCI procedure, such as the deployment of a stent) and to collect biomarker gradients released locally within the coronary artery. It will then follow up on the health status of the patients and see if the release of certain biomarkers is associated with particular clinical outcomes. The device will be used to look for locally released biomarkers at two different stages of the deployment of a stent, i.e. before and after its deployment. The first stage is prior to the deployment of the stent and the LBS will collect blood samples to look for the release of "natural" biomarkers gradients, i.e. those biomarkers that are naturally released during the progression and development of diseased regions within the artery. The second stage is to use the LBS to collect blood samples across a diseased artery that has just be perturbed (by "pre-ballooning", a procedure carried out just prior to stent insertion) and will looked for "induced" biomarker gradients, i.e. those molecules that are released by a diseased plaque when it ruptures. The insights gained by collecting biomarker gradients at these two stages will give very important information on what causes a region of artery to become diseased and how diseased portions of the artery affect the blood and cause heart attacks. The samples that are collected by the LBS in the above clinical settings will be analysed for a series of biomarker gradients previously selected by PlaqueTec' s Scientific Advisory Panel (SAP) for their potential role in causing atherosclerosis. The data collected by the LBS will be for research only and will not be used to affect the patient treatment. In summary, the LBS study will deliver completely new insights into coronary artery disease and will significantly increase the understanding of this hugely significant disease. Patients who need an elective percutaneous transluminal interventional coronary procedure will be considered for this study. Patients requiring emergency interventional procedures will be excluded. The study duration is estimated to be about 8 months with a three year follow up period.