Effects of pulsating frequency and amplitude on the flow structure and mixing of a heated axisymmetric subsonic jet have been examined by direct solution of the compressible Navier-Stokes equations using highly accurate numerical methods. The organized unsteadiness associated with the periodic pulsation leads to a variety of vortical structures in the pulsating flow field. It is found that the vortical structures become smaller with increased pulsating frequency. At a high enough pulsating frequency, the jet is underexpanded near the nozzle and it does not develop large-scale vortical structures downstream. It is also found that pulsating amplitude has a strong effect on the flow structure and that vortex pairing occurs at relatively low pulsating amplitudes. The simulations show that lower pulsating frequency and larger pulsating amplitudes lead to stronger jet mixing with the ambient and faster decay of temperature.