Development of the mammalian cardiovascular system is a complex process guided by both genetic and environmental components. Significant advances in the genetics of vascular development have been accomplished most recently by the analysis of multiple "knockout" and transgenic mice which exhibit varying degrees of impaired vascularity. This review focuses on the potential of the environment of the developing embryo to affect its development. In particular we analyze the evidence implicating the ability of physiological parameters such as oxygen and glucose concentrations within and surrounding the embryo to affect the expression of genes critical for vascular development. We conclude that the vascularization of a developing mammalian embryo is a plastic process dependent on the dynamic interaction between fundamental genetic and physiological factors.