Effect of heavy cation doping (Ca2+ at the A-site) on the thermal properties of perovskite LaMnO3 has been investigated using the Rigid Ion Model (RIM)). As strong electron-phonon interactions are present in these compounds, the lattice part of the specific heat deserves proper attention. The specific heat of magnetoresistance compound La0.25Ca0.75MnO3 as a function of temperature (10 K ≤ T ≤ 300 K) is reported. Our results on specific heat are in good agreement with the measured values of specific heat at lower temperatures. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Restrahalen frequency (ν 0), Debye temperature (Θ D) and Gruneisen parameter (γ) are also discussed.