  On the basis of consistent stellar evolution and nonlinear stellar pulsation
calculations the Cepheid V1033 Cyg is shown to be the post--main sequence star
at the first crossing of the instability strip during gravitational contraction
of the helium core. The observed light variability of V1033 Cyg is due to
radial oscillations in the fundamental mode. The best agreement (within one
percent) between recent observations and the theoretical estimate of the period
change rate was obtained for the evolutionary sequence with stellar mass
$M=6.3M_\odot$ and helium and heavier element fractional abundances $Y=0.28$
and $Z=0.022$, respectively. The age of the star, the luminosity, the radius,
the effective temperature and the surface gravity are $t_\mathrm{ev}=5.84\times
10^7$ yr, $L=2009L_\odot$, $R=45.6R_\odot$, $T_\mathrm{eff}=5726 \mathrm{K}$,
$\log g=1.92$.
