Dementia with Lewy bodies (DLB) is a neurodegenerative condition that results in loss of mesopontine cholinergic neurons and sympathetic deinnervation. Although acetylcholinesterase inhibitors have been shown to improve cognitive and behavioral deficits in DLB, these patients may be more susceptible to bradyarrhythmic side effects from this class of drugs due to the autonomic insufficiency associated with the disease. We present a patient who experienced a dose-dependent, symptomatic sinus bradyarrhythmia with donepezil doses at and greater than 5 mg. Owing to underlying autonomic dysfunction, patients with DLB may be at increased risk of bradyarrhythmia resulting from treatment with acetylcholinesterase inhibitors.