  We present a search for anomalous semileptonic decays of heavy flavor hadrons
produced in association with a $W$ boson, in proton-antiproton collisions at
sqrt{s}=1.96 TeV. We use 162 pb-1 of data collected with the CDF II detector at
the Fermilab Tevatron Collider. We select events with one W boson and at least
one jet with an identified secondary vertex. In the jets with a secondary
vertex we look for a semileptonic decay to a muon. We compare the number of
jets with both a secondary vertex and a semileptonic decay, and the kinematic
properties of these jets, with the standard model expectation of W plus heavy
flavor production and decay. No discrepancy is seen between the observation and
the expectation, and we set limits on the production cross section of a B-like
hadron with an anomalously high semileptonic branching ratio.
