  We present the results of the radial velocity ($RV$) measurements of metallic
lines as well as H$_{\alpha}$ (H$_{\beta}$) obtained in 55 high-resolution
spectra of the Cepheid $\alpha$ UMi (Polaris Aa) in 1994-2010. While the $RV$
amplitudes of these lines are roughly equal, their mean $RV$ begin to differ
essentially with growth of the Polaris Aa pulsational activity. This difference
is accompanied by the H$_{\alpha}$ line core asymmetries on the red side mainly
(so-called knife-like profiles) and reaches 8-12 km/s in 2003 with a subsequent
decrease to 1.5-2 km/s. We interpret a so unusual behaviour of the H$_{\alpha}$
line core as dynamical changes in the envelope around Polaris Aa.
