Angiogenesis is a physiological process in organ development and also a compensatory response in ischemia. When ischemia occurs, oxygen sensors in vascular endothelial cells sense the decrease in oxygen, thus activating downstream signaling pathways to promote the proliferation, migration, and tube formation of the endothelial cells. The new vasculatures are formed by sprouting from preexisting vessels, in order to maintain oxygen homeostasis in ischemic tissues (Folkman and Shing 1992). Collateral circulation is sometimes established under chronic ischemic conditions such as chronic myocardial ischemia (Banai et al. 1994). However, naturally occurring angiogenesis is usually not sufficient to compensate for ischemia in ischemic tissues. Proangiogenic drugs may be useful to promote angiogenesis in these diseases.