A 67-year-old woman with idiopathic orthostatic hypotension was presented. The patient started to experience faintness on standing since 1993. During a physical examination, her systolic blood pressure fell from 148 to 50 mmHg on standing. Blood pressure responses to the mental arithmetic test and hyperventilation stress were normal. However, cold pressor test failed to increase blood pressure. These observations, with the finding that phase IV response on Valsalva's maneuver was absent, indicate afferent sympathetic nervous dysfunction. Peripheral neuropathy including diabetes mellitus and involvement of central nervous system such as multiple system atrophy were excluded. Holter ECG examination revealed a 3.9 second sinus arrest and bradycardia (total beats 88901/day). the blunted responses of the heart rate to atropine as well as isoproterenol further suggested the presence of sick sinus syndrome. Amezinium administration significantly improved her orthostatic hypotension and eliminated sinus arrest. These findings indicate that sympathetic nervous dysfunction could account for at least a part of the sick sinus syndrome in this patient.