  We review the general properties of the intracluster medium (ICM) in clusters
that host a cooling flow, and in particular the effects on the ICM of the
injection of hot plasma by a powerful active galactic nucleus (AGN). It is
observed that, in some cases, the hot plasma produces cavities in the ICM that
finally detach and rise, perhaps buoyantly. The gas dynamics induced by the
rising bubbles can help explain the absence of a cooled gas component in
clusters with a cooling flow. This scenario is explored using numerical
simulations.
