Is dynamic heating of stellar disk inevitable?
  Major mergers or/and the repeated minor mergers lead to dynamical heating of
disks of galaxies. We analyze the available data on the velocity dispersion of
stellar disks of S-S0 galaxies, including the new observational data obtained
at 6m telescope of SAO RAS. As a measure of dynamical (over)heating, we use the
ratio of the observed velocity dispersion to the minimal dispersion which
provides the local stability of the stellar disks with respect to gravitational
perturbations. We came to conclusion that stellar disks in a significant part
of galaxies (including LSB and some S0 galaxies) are close to the marginal
stability condition (or are slightly overheated) -- at least at radial
distances $r\sim$ 2-3 radial scalelenghts. It enables to constrain the role of
merging in the heating of stellar disks: in many cases it seems to be
non-efficient. Marginal stability condition may also be successfully used to
estimate the mass of a disk and the midplane volume gas (stars) densities on
the basis of kinematic measurements.
