Convection in astrophysical systems is stratified and often occurs at high Rayleigh number (Ra) and low Mach number (Ma). Here we study stratified convection in the context of plane-parallel, polytropically stratified atmospheres. We hold the density stratification ($n_{ρ}$) and Prandtl number (Pr) constant while varying Ma and Ra to determine the behavior of the Nusselt number (Nu), which quantifies the efficiency of convective heat transport. As Ra increases and $\text{Ma} → 1$, a scaling of Nu $∝$ Ra$^{0.45}$ is observed. As Ra increases to a regime where Ma $≥ 1$, this scaling gives way to a weaker Nu $∝$ Ra$^{0.19}$. In the regime of Ma $≪ 1$, a consistent Nu $∝$ Ra$^{0.31}$ is retrieved, reminiscent of the Nu $∝$ Ra$^{2/7}$ seen in Rayleigh-Bénard convection. ; Comment: Submitted to PRL