  Explicit quark-hadron duality in the limit of heavy quark mass is studied
using the 't Hooft model, where both partonic and hadronic amplitudes may be
computed exactly. Results for weak decays of heavy mesons are presented for
both standard spectator decays, where the duality limit is convincingly
approached, and annihilation decays of the valence quark-antiquark pair, where
the approach to asymptotic duality is much less precise.
