Left, Functional vascularization of an ischemic myocardial region requires both capillary angiogenesis and coronary arteriogenesis (including the growth of preexisting collaterals). New capillaries become perfused and able to delivery oxygen only when they connect to the existing coronary vasculature. Coronary arteriogenesis will increase the total amount of flow to the ischemic region, whereas capillary angiogenesis improves distribution of the flow and oxygenation of the individual cardiomyocytes. Right, Transplantation of VEGF-expressing myoblasts into the myocardial walls of mice results in the formation of a hemangioma (‘angioma-genesis’) and death of these mice. The new capillaries that from in this area are fragile, lack smooth muscle cells and are susceptible to rupture. Furthermore, when they fail to connect to the existing coronary vasculature, they regress. EC, endothelial cell; SMC, smooth muscle cell.