Novel heterocyclo compounds useful as inhibitors of potassium channel function (especially inhibitors of the K.sub.v1 subfamily of voltage gated K.sup.+ channels, especially inhibitors K.sub.v1.5 which has been linked to the ultra-rapidly activating delayed rectifier K.sup.+ current I.sub.Kur), methods of using such compounds in the prevention and treatment of arrhythmia and I.sub.Kur-associated conditions, and pharmaceutical compositions containing such compounds.