A numerical study is conducted to investigate the transport mechanism of laminar mixed convection in a shear- and Buoyancy-driven cavity having a locally heated lower wad and mooing cooled sidewalls. Effort is focused on the interaction of forced convection with natural convection. Localized heating is simulated by a centrally located heat source on the bottom wall, and four different values of the dimensionless heat source length, epsilon, 1 / 5, 2 / 5, 3 / 5 and 4 / 5 of the nondimensional length of the bottom wall, are considered. parametric studies on the effect of mixed convection parameter, Gr / Re-2 (also referred to as Richardson number, Ri), in the range 0.1-10, on the fluid flow and heat transfer are performed for each epsilon. Local results are presented in the form of streamline and isotherm plots as well as the variation of local Nusselt number on the heated wall. Three different regimes are observed with increasing Gr / Re-2:forced convection (with negligible natural convection), mixed convection (comparable forced and natural convection), and natural convection (with negligible forced convection).