Accordingly, the aim of this study is to carry out the first prospective assessment of the significance of subpopulations of circulating EPCs in the subsequent occurrence of restenosis or progression of coronary atherosclerosis after PCI. To this end, a pool of EPCs subtypes that are suggested to play some role in atherosclerosis is measured in a homogenous population of candidates to PCI. At variance with previous work, counts of EPCs are obtained in baseline conditions before PCI in order to avoid the confounding effect that the procedure exerts on EPCs.