Analyses of the light variation of the 6 Scuti star CC Andromedae and of the radial velocity variation of the ß Canis Majoris star 6 Scorpii, a single -line spectroscopic binary, indicate that the long period modulations exhibited are caused by tidal deformations induced in the hydrogen and /or helium ionization zones of each primary by a faint companion, resulting in surface zonal variations of the amplitude and phase of each primary's normal radial pulsations. The variations in the tide raising potential calculated at the center of the apparent disk of o Scorpii correlate very strongly with the observed variations in the phase zero -point of the fundamental pulsation. It is suggested that all the ß Canis Majoris and 6 Scuti stars exhibiting long period modulation, and probably also the RR Lyrae stars showing a Blazhko effect, do so because of tidal perturbations induced by faint companions.