A 45-year-old Nobel Prize-winner in chemistry has recently been the recipient of a heart transplant. Patient education has included both verbal and written descriptions of the potential cardiovascular effects of pharmacologic agents. Which one of the following drugs is least likely to cause tachycardia in this patient?

This question is to remind you that indirect-acting sympathomimetics require innervation of the effector organ to exert effects. In this case, amphetamine would not be effective because the transplanted heart lacks sympathetic innervation; thus, there is no "mobile pool" of NE capable of being released by a drug. However, transplanted hearts retain receptors, including those (b1 ) responsive to direct-acting sympathomimetics. Heart transplants are not responsive to AChE inhibitors because they, too, are indirect acting and require vagal innervation to exert effects on the heart.