The present reexamination of the problem of ISM heating via the damping of plasma irregularities responsible for interstellar scintillations of radio sources gives attention to the effects of recent observational results on the hot plasma of the irregularities and on developments of in the theory of MHD waves. The damping mechanisms considered are linear Landau damping, ion-neutral collisional damping, nonlinear steepening of wave packets, a parametric decay instability, and nonlinear Landau damping. The heat input from all damping mechanisms can be accommodated by the 'fluctifer' region containing the irregularities, if it has features similar to the extended H II envelopes.