  The latest experimental results in relativistic heavy-ion collisions show
that the matter there produced requires transport coefficients because of the
important collective properties found. We review the theoretical calculation of
these transport coefficients in the hadron side at low temperatures by
computing them in a gas composed of low energy pions. The interaction of these
pions is taken from an effective chiral theory and further requiring scattering
unitarity. The propagation of D and D* mesons in the thermalized pion gas is
also studied in order to extract the heavy quark diffusion coefficients in the
system.
