Previous reports1-4 have presented the primary relation of hemodynamics to the inherent pathology of atherosclerosis. The hemodynamic concept of atherosclerosis considers the laws of fluid dynamics as the primary factor in the pathogenesis of atherosclerosis. The laws of fluid mechanics can account for the inception, the progressive changes, and the varied pathologic appearances of arterial occlusive disease in the aorta and coronary arteries as well as in arteries of the viscera and extremities. The absence or lesser degree of atherosclerosis in the pulmonary artery and in veins is also accounted for on the basis of hemodynamics. The hemodynamic concept of atherosclerosis was developed by correlating atherosclerotic lesions found at autopsy with their localization as determined by hydraulic principles. It was then demonstrated with the aid of model hydraulic systems built to the precise specifications of blood vessels obtained at autopsy. Flow in these models, as well as in the