Patients w/ pre-existing abnormalities in SA & AV node activity; congenital or documented acquired QT prolongation; poor cardiac reserve; unstable angina pectoris; recent MI. Concomitant use w/ medications that prolong the QT interval eg, class I & III antiarrhythmics, TCAs, some antipsychotics, antibiotics (eg, erythromycin) & some antihistamines (eg, terfenadine). Patients w/ hepatic impairment. Pregnancy & lactation. No experience of use in childn.