A polycrystalline Pb(ZrTi)O3 (PZT) film with Pb excess is considered as a heterophase medium that consists of PZT grains and semiconductor PbO phase. The latter is segregated on PZT grain boundaries during the PZT formation and forms conducting channels between the electrodes. In such medium, uncompensated polarization charge of PZT grains generates an electric field both inside PZT grains and PbO phase. This electric field affects on ferroelectric polarization itself and stimulates carrier transport through the PbO channels. A theory is developed, where the reciprocal effect of the electric field on the polarization is taken into account. The polarization is found due to this effect to be increased up to ∼30% near the interfaces, which differs from reduction of the polarization near the interfaces in homogeneous PZT films. Using the theory, the electric field, electrostatic potential and carriers transport in PbO channels are calculated. A comparison is made with the results calculated for the approach of the polarization constancy.