Human Cardiac microvascular endothelial cells (CMEC) play important roles in myocardial function. They regulate vascular tone by releasing and degrading endothelium-derived vasoactive factors, and modulating the local levels of vasoconstrictors and vasodilators through their enzymatic activities. Many of these substances can also modify myocardial contractile behavior. Furthermore, microvasculature participates in the regulation of leukocyte recruitment, inflammation, and angiogenesis. They are also capable of trans-differentiating into myofibroblasts, suggesting a role in aberrant accumulation of matrix and fibrotic disorders. Human Cardiac Endothelial Cells provide an invaluable tool for understanding CMEC physiological and pathophysiological relevance in cardiac function and disease