The endothelial cells modulate vascular tone by release of several endothelium-derived contracting and relaxing factors, by regulation and degradation of vasoactive peptides, and by enzymes located on the endothelial surface. These functions vary within different spaces, within blood vessels of different organs, and between the macro- and microvasculations. Cardiac microvascular endothelial cells (CMEC) exert physiological and pathophysiological effects on the function of cardiac myocytes. They release cardioactive substances including nitric oxide, endothelin-1, prostanoids, adenylpurines, natriuretic peptides, and other agents, that modify and regulate cardiac myocyte function. Such effects of endothelial cells have been demonstrated both in vivo and in vitro. CMEC also possess enzymatic activities, in particular ACE/kininase activity, which can alter local levels of angiotensin II and bradykinin in the heart. HCMEC from AcceGen Biotech Research Laboratories are isolated from human heart tissue. HCMEC are cryopreserved after purification and delivered frozen. Each vial contains >5 x 10^5 cells in 1 ml volume. HCMEC are characterized by immunofluorescent method with antibodies to vWF/Factor VIII and CD31 (P-CAM) and by uptake of DiI-Ac-LDL. HCMEC are negative for HIV-1, HBV, HCV, mycoplasma, bacteria, yeast and fungi. HCMEC are guaranteed to further expand for 15 population doublings at the conditions provided by AcceGen Biotech Research Laboratories.