Recent X-ray observations of galaxy clusters have shown that the density of the intracluster gas is lower (or equivalently, its entropy is higher) than expected from simple theoretical considerations. This is especially so in the case of groups of galaxies. These observations require some non-gravitational heating of the intracluster gas. We discuss the role of active galaxies as a source of heating and explaining the observations of excess entropy. We also discuss the implications of such heating for the CMB power spectrum.