The study of laminar flow and heat transfer occurring over a stretching sheet in a viscous fluid is of considerable interest because of their ever increasing industrial applications and important bearings on several technological processes, the present study focused on investigating the unsteady magneto hydrodynamic flow of Casson fluid accompanied by heat transfer through parallel plate. The investigation reveals many important aspects of flow and heat transfer. The flow features and heat transfer characteristics for different values of the governing parameters viz. Casson parameter, heat source parameter, Hartmann number, and Prandtl number are analysed and discussed in detail. It was found that heat source and magnetic field modify the flow patterns and increase the temperature of the fluid.