(LVEF < 45% as determined by MUGA scan or echocardiogram, Complete left bundle branch block, Obligate use of a cardiac pacemaker, Congenital long QT syndrome, History or presence of ventricular tachyarrhythmia, Presence of unstable atrial fibrillation (ventricular response > 100 bpm). Patients with stable atrial fibrillation are eligible, provided they do not meet any of the other cardiac exclusion criteria, Clinically significant resting bradycardia (< 50 bpm), Uncontrolled hypertension (systolic blood pressure 150 mmHg and/or diastolic blood pressure 100 mmHg, with or without anti-hypertensive medication)., QTc > 480 msec on screening ECG, Right bundle branch block + left anterior hemiblock (Bifascicular block), Angina pectoris 3 months prior to starting study drug, Acute Myocardial Infarction 3 months prior to starting study drug, Other clinically significant heart disease (e.g., Congestive heart failure, history of labile hypertension, or history of poor compliance with an antihypertensive regimen))