Abstract: Compounds of formula (I) and pharmacologically acceptable salts thereof wherein: n is 1 to 3, R is an alkyl, R.sub.1 is hydrogen or alkyl, R.sub.2 is alkyl, R.sub.3 is an alkyl; b) alkyl substituted with an aryl, heteroaryl or cycloalkyl; c) alkyl substituted with one to eight fluorine atoms; d) cycloalkyl; e) alkenyl; f) alkyl substituted with one to three hydroxy, acyloxy or alkoxy substituents, and where the sum of carbons in R.sub.2 and R.sub.3 is greater than five br where R.sub.2 and R.sub.3 with the nitrogen atom form a saturated heterocyclic group having one nitrogen and form 4-8 carbon atoms or a 4-substituted piperazine group in which the 4-substituent can be alkyl, aryl, benzyl, or heteroaryl, and X is hydrogen, hydroxy, alkoxy, alkyl, carbon trifluoride or a halogen, or compounds of formula (I') and pharmacologically acceptable salts thereof wherein: n is 1 to 3, R is an alkyl, R.sub.1 is hydrogen or alkyl, R.sub.2 is an alkyl, R.sub.

Abstract: Methanesulfonamides are structurally depicted by Formula I' ##STR1## or its pharmacologically acceptable salts where R.sub.3 is a C.sub.1-7 alkyl substituted with C.sub.3-7 cycloalkyl, or a C.sub.1-10 alkyl substituted with one to eight fluorine atoms, one to three hydroxy, one to three C.sub.1-5 acyloxy or one to three C.sub.1-4 alkoxy substituents. These compounds are useful as Class III antiarrhythmic agents and are stable against rapid metabolism. Methods for treating cardiac arrhythmias with the compounds of Formula I' as well as compositions thereof are also described.