Compounds of formulae: where Ar.sub.1, Ar.sub.2, R.sub.3, R.sub.4, and m are disclosed herein, or a pharmaceutically acceptable salt thereof (a "Nitro(cyano)vinylpiperazine Compound"); compositions comprising an effective amount of a Nitro(cyano)vinylpiperazine Compound; and methods for treating or preventing pain and other conditions in an animal comprising administering to an animal in need thereof an effective amount of a Nitro(cyano)vinylpiperazine Compound are disclosed.