Patients having atrioventricular block 2nd- and 3rd-degree or sinoatrial block; pregnant women and women suspected of being pregnant; patients with sick sinus syndrome except in the presence of a functioning ventricular pacemaker; hypotension (<90 mm Hg systolic); patients who have demonstrated hypersensitivity to the drug; those with acute myocardial infarction and pulmonary congestion documented by x-ray on admission.