Perioperative beta(1)-selective-adrenergic antagonist administration has been shown to decrease morbidity and mortality in patients with cardiac disease undergoing surgical procedures. We report a case of a patient receiving the selective beta(1)-adrenergic antagonist, metoprolol, immediately before surgery that was associated with severe hypoglycemia. We postulate that an underlying abnormality in energy requirements or metabolism may allow for beta(1)-selective-adrenergic antagonists to precipitate hypoglycemia.