The invention provides compounds of the formula: wherein R1 is aryl, heteroaryl, cycloalkyl or alkyl; R2 is H, alkyl, nitro, CO2R7, CONR5R6 or halo; R3 and R4 are H, NR5R6, NC(O)R7, halo, trifluromethyl, alkyl, CONR5R6, CO2R7, nitrile or alkoxy; R5 and R6 may be the same or different and may be H, alkyl, aryl, heteroaryl or cycloalkyl; or R5 and R6 may together form a saturated, unsaturated or partially saturated 4 to 7 member ring, wherein said ring may optionally comprise one or more further heteroatoms selected from N, O or S; R7 is H or alkyl; A is H, halo, or a group of formula X-L-Y; X is O, S or NR8; R8 is H or alkyl; L is (CH2)n, where n is 0, 1, 2, 3 or 4; and Y is aryl, a heterocyclic group, alkyl, alkenyl or cycloalkyl; the products of mono- and di-oxidation of sulphur and/or mono-oxidation of nitrogen moieties in compounds of formula I; or a pharmaceutically acceptable salt thereof. These compounds find use as inhibitors of potassium ion channels and thus are useful in the treatment of various conditions including arrhythmia and type-2 diabetes mellitus.