The mechanism of vortex shedding behind the cylinder, first observed by Von K`arm`an, is still an open question. At very low Reynolds numbers, (defined as Re=U0D/ ), wake region behind the cylinder appears as a symmetrical twin vortex. Under certain condition these coherent structures advect down stream. A vortex street appears at 45<Re<180. Several investigations have been carried out to determine the effects of external sources on the vortex shedding process and the associated wake properties. In the present study we attempt to elucidate numerically the effect of heat on vortex shedding and coherent structures. The heating of cylinder generates an asymmetry in the flow because of stable and unstable region developed at the bottom and top side respectively. We propose to study the effect of heat flux on vortex shedding and vortex structure at low Reynolds number in a twodimensional incompressible.