The temperature dependence of the velocity of sound is calculated for heavy fermions within a mean field approach. The basic parameters of the periodic Anderson model, V and E_O, are taken to be volume dependent. This leads to a volume dependence of the chemical potential, mu , the renormalized f level energy, epsilon /sup /f, the number of f electrons, n_f, and the renormalized hybridization V. These effects are all included in the calculation of the temperature dependence of the sound velocity.