Hypersensitivity, Sick sinus syndrome (unless the Pt. has a functioning pacemaker), Second- or third-degree heart block. Sinus bradycardia, Hypotension, Cardiogenic shock, Severe congestive heart failure, Wolff-Parkinson-White syndrome with atrial fibrillation or flutter. Pt. receiving IV beta blockers. Give with extreme caution to Pt. receiving oral beta blockers. Wide-complex tachycardias of uncertain origin (ventricular tachycardia can deteriorate into ventricular fibrillation when calcium channel blockers are given.)