Dementia with Lewy bodies (DLB) is recognized as the second most common form of dementia in aged people. It is well known that patients with DLB often develop various autonomic symptoms. Here, we present a case in which there was sick sinus syndrome mimicking the DLB-related autonomic dysfunctions. After the pacemaker implantation, the patient's symptom perfectly extinguished. It is essential for psychiatrists or other professionals who are mainly seeing dementia patients to rule out critical causes that may mimic autonomic symptoms in patients with DUB.