<p>Disclosed is a compound represented by the formula shown below and a pharmaceutically acceptable salt thereof, which is useful as an IKur-blocker that is useful for the prevention or treatment of cardiac arrhythmia such as atrial fibrillation. wherein the ring X represents a benzene or a pyridine; R1 represents a substituted alkyl; R2 represents an aryl which may be substituted or a heterocyclic group which may be substituted; R3 represents a hydrogen or an alkyl; R4 represents a hydrogen, a halogen or an alkyl; R5 represents a hydrogen or an alkyl; and R6 and R7 independently represent a hydrogen or a halogen.</p>
