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Figure 1: Schematic representation of the distribution of coronary vascular resistance and the mechanisms that contribute to control of resistance in successive segments of the coronary vascular tree. The majority of resistance resides in large, intermediate, and small arterioles. Distal small arterioles are most sensitive to changes in intraluminal pressure and contribute the most to coronary autoregulation. Intermediate arterioles are most responsive to cardiac metabolites, contributing substantially to metabolic regulation of coronary flow. Small resistance arteries and large arterioles demonstrate the greatest responsiveness to intraluminal flow.