Objectives Endothelial progenitor cells (EPCs) play a key role in maintenance of endothelial integrity and postnatal neovascularization. We verified whether the number of subpopulations of EPCs is different in patients with coronary artery disease (CAD) and normal or impaired left ventricular 0) function. Methods Sixty-eight consecutive patients (37 men, age 60 18 years) with CAD were studied. All patients underwent quantitative coronary angiography and flow cytometric analysis. Results Patients with LV ejection fraction <45% (n=22) were compared with those with normal function 0=46). The two groups had similar age, sex, cardiovascular risk factors, medical therapy, LV dimension, and number of diseased vessels. Patients with LV dysfunction, by study design, were more symptomatic and had a lower LV ejection fraction. The two groups had similar white cell count and mononuclear cells. The absolute number of CD34(+) and CD133(+) cells was significantly (P<0.05) higher in patients with LV dysfunction as compared with patients with normal function or healthy participants. In contrast, CD14(+) cells were significantly (P=0.005) lower in the former patients than in the latter, whereas no significant difference was noted in the number of cells positive for CD105 among groups. Conclusion Subpopulations of EPCs have a discordant behavior in CAD patients with or without LV dysfunction, with cells positive for the endothelial markers CD34 and CD133 being increased and cells that promote vasculogenesis and microvascular development being significantly reduced. Coron Artery Dis 20:303-308 (C) 2009 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.