The synthesis and Claw Ill antiarrhythmic activity of a seriea of 4 [(methylsulfonyl) amino] be&des and sulfonamides are described. Selected compounds show a potent Class I11 activity and are devoid of effects on conduction both in vitro (dog Purkinje fibers) and in vivo (anesthetized dogs). Compounds having a 2-aminobenzimidazole group were found to be the most potent, and one compound having this heterocycle (5, WAY-123,398) was ...