The compounds are of the heterocyclic class of 2-phenethylpiperidines having an amido substituent in the ortho position of the phenethyl moiety. Substituents in the ortho position include formamido, benzamido, cinnamamido, 2-thiophenecarboxamido, alkanesulfonamido and alkanoylamido. They are useful as antiarrhythmic and/or antiserotonin agents. The novel compounds are prepared by reaction of appropriately substituted o-aminophenethylpiperidines and the carbonyl or sulfonyl halides or anhydrides. Typical embodiments of this invention are 4-methoxy-2'-[2-(1-methyl-2-piperidyl)ethyl]benzanilide and 2'-[2-(1-methyl-2-piperidyl)ethyl]cinnamanilide.