  We improve the excluded volume hadron resonances gas model (EHRG) to cure the
acausal behavior of the sound velocity which is typical of excluded volume
models. We achieve this by including temperature (T) and density ({\mu})
dependent hadron masses in the partition function of EHRG. The temperature and
density dependent masses of the constituent quarks (u,d,s) and the light mesons
are obtained within Nambu-Jona-Lasinio model while for the heavy hadrons we use
linear scaling rule in terms of constituent quarks. With this improvement, we
observe that the velocity of sound flattens at high temperature unlike old EHRG
models where the sound velocity rises very rapidly at high temperatures which
is the indication of its super-luminal behavior.
