- Myocardial infarction within 3 months, unstable angina within 3-5 days prior to starting infusion, unstable supra-ventricular and/or ventricular arrhythmia, severe conduction defect (AV block grades 2 and 3), complete left or right Bundle Branch Block, bradycardia (heart rate [HR] less than 50 bpm), uncompensated heart failure