  In the present paper, the effects of viscous dark matter are analysed within
the $\Lambda$CDM model. Here we consider bulk viscosity through the
Israel-Stewart theory approach, leading to an effective pressure term in the
continuity equation that accomplishes for the dissipative effects of the dark
matter fluid. Then, the corresponding equation for viscosity is solved and a
general equation for the Hubble parameter is obtained with the presence of a
cosmological constant. The existence of de Sitter solutions is discussed, where
a wider range of solutions is found in comparison to the $\Lambda$CDM model.
Also the conditions for the near thermodynamical equilibrium of the fluid is
analysed. Finally, a qualitative analysis provides some constraints on the
model by using Supernovae Ia data which reveals the possible importance of
causal thermodynamics in cosmology.
