Endothelial progenitor cells (EOCs) play a key role in reendothelization of injured blood vessels and in endogenous neovascularization of ischemic tissues. In the presented article, the mechanisms of endothelial function impairment and the role of EPCs in their correction are discussed. The objective of our study was to investigate the number of CD34+ cells in patients with different forms of ischemic heart disease (IHD) and association of this parameter with endothelial dysfunction. We quantified the numbers of CD34+ cells by flow cytometry, measured the brachial artery flow-mediated vasodilatation (FMD) and the common carotid artery intima-media thickness (IMT) by ultrasonography in 28 patients with ST-segment elevation acute coronary syndromes (ACS), in 33 patients with stable angina (SA) and in 17 subjects without IHD (control group). The level of CD34+ cells was lower in both groups of IHD, especially in patientes with ACS, and was associated with endothelial dysfunction. We suppose that CD34+ cells contribute to reparation of injured endothelium and the reduction of their numbers in peripheral blood indicates endothelial state.