  We propose a modification of the hydrodynamic model of the dynamics in
ultrarelativistic nuclear collisions. A modification of the energy-momentum
tensor at the initial stage describes the lack of isotropization of the
pressure. Subsequently, the pressure is relaxing towards the equilibrium
isotropic form in the local comoving frame. Within the Bjorken scaling solution
a bound is found on the decay time of the initial anisotropy of the
energy-momentum tensor. For the strongest dissipative effect allowed, we find a
relative entropy increase of about 30%, a significant hardening of the
transverse momentum spectra, and no effect on the HBT radii.
