The heat generated by viscous dissipation is consistently evaluated using a 2-D compressible subduction model with variations of mantle rheology (constant as well as pressure and temperature dependent viscosity), dip, age, and velocity of the subducting slab. For comparison, we also conduct 2-D incompressible subduction calculations with the same conditions and parameters used in the compressible formulation. The effect of compressibility on the thermal and flow structures of the subduction zones is relatively small and concentrated along the base of the mantle wedge, with temperature differences <100°C and differences in kinematic energy of the mantle wedge <1% between compressible and incompressible models. Mantle rheology has a stronger effect on thermal and flow structures than mantle compressibility as well as the variations of dip, age, and velocity of the subducting slab. The heat from viscous dissipation in the compressible model increases the slab temperatures over the incompressible model (<70°C), as a result of additional conduction across the slab surface (constant viscosity) and thinning of the thermal boundary layer caused by viscosity reduction (pressure- and temperature-dependent viscosity).