An IKr inhibitor (IC50 40 nM in isolated rabbit sinoatrial node cells) selective for IKr over L-type Cav current and If at 1 UM decreases the diastolic depolarization rate and increases cycle length and action potential duration at full repolarization in isolated rabbit sinoatrial node cells at 50 nM decreases the QT interval and increases heart rate in anesthetized guinea pigs at 1 mg/kg decreases the time to first arrhythmia and ventricular fibrillation in ouabain-stimulated guinea pigs at 1 mg/kg