We discuss the applicability of the perturbative QCD formalism, which includes the resummation of large radiative corrections, to B meson decays, concentrating on the semileptonic decay B→πlv. It is found that the perturbative QCD analysis of this process is reliable for the energy fraction of the pion above 0.4. Combining predictions from soft pion theorems, we estimate that the upper limit of the matrix element lVubl is 2.8 - 4.8 x 10^-3 from different models of B meson wave functions.