Fluid shear stress is an important determinant of cardiovascular development and pathology. When shear stress levels alter, vascular tone changes through the release of endothelin-1 and nitric oxide, and endothelial cells react by either increase or decrease of gene expression, probably through activation of shear stress responsive promoter elements. We generated a model (venous clip) with altered shear stress in a chicken embryo resulting in cardiovascular malformations. We generated physiological data (flow velocity, pressure, volume) on the performance of the chicken embryonic heart during normal and abnormal development. These data are fed into a custom made Computational Fluid Dynamics model of the beating embryonic heart in which it is possible to predict "hotspots" of shear stress changes during the various phases of contraction. MicroPIV shows a parabolic velocity distribution in embryonic vessels. Levels and patterns of expression of key regulatory genes have been studied during various stages of (ab)normal development. Furthermore, shear dependent endothelial function and differentiation was determined by immunostaining and QPCR. This research was supported by NHF2000.016.