In circulatory system, the highest velocity of blood flow is in the aoa. The velocity of blood flow is inversely propoional to vascular cross-sectional area. v=Velocity F= Blood flow through the area A= Vascular cross sectional area Aoa has the least cross sectional area (4.5 cm2) and capillaries have the maximum cross sectional area (4500 cm2). Thus, under resting conditions, the velocity is highest in aoa and least in capillaries. Ref: Guyton and Hall 13th edition Pgno: 169-170