  We present a general method that allows one to decay narrow resonances in Les
Houches Monte Carlo events in an efficient and accurate way. The procedure
preserves both spin correlation and finite width effects to a very good
accuracy, and is therefore particularly suited for the decay of resonances in
production events generated at next-to-leading-order accuracy. The method is
implemented as a generic tool in the MadGraph framework, giving access to a
very large set of possible applications. We illustrate the validity of the
method and the code by applying it to the case of single top and top quark pair
production, and show its capabilities on the case of top quark pair production
in association with a Higgs boson.
