  We discuss the leading order of anisotropic hydrodynamics expansion. It has
already been shown that in the (0+1) and (1+1)-dimensional cases it is
consistent with the second order viscous hydrodynamics, and it provides a
striking agreement with the exact solutions of the Boltzmann equation. Quite
recently, a new set of equations has been proposed for the leading order of
anisotropic hydrodynamics, which is consistent with the second order viscous
hydrodynamics in the most general (3+1)-dimensional case, and does not require
a next-to-leading treatment for describing pressure anisotropies in the
transverse plane.
