Familial atrioventricular heart block affected by the autonomic nervous system has rarely been documented. We describe a 35-year-old man who had first-degree atrioventricular heart block with a PR interval of 0.46 s. He had a family history of 2 members with complete heart block and 1 with documented atrial standstill. The man's P-R interval was shortened by exercise and phenylephrine administration. In the electrophysiolgic study, a "split His" with an H-H' of 220 ms was recognized. Such a case of familial atrioventricular heart block with abnormal His-Purkinje conduction affected by the autonomic nervous system is very rare and worthy of description.