A 10-year-old boy is reported who presented with idiopathic atrial fibrillation and bradyarrhythmia. After history of intrauterine and postnatal bradycardia, atrial fibrillation was first documented electrocar-diographically at 16 months of age. An underlying structural heart disease was not evident. At the age of 10 years, implantation of a permanent ventricular demand pacemaker was indicated after syncope due to severe bradyarrhythmia. The family history revealed five persons of four generations with bradyarrhymias. Idiopathic atrial fibrillation known since childhood was documented in three close relatives. A high grade AV block resulting in bradyarrhythmias and the occurrence of ST-T-changes in precordial leads could be demonstrated in all affected family members suggesting a diffuse general conduction abnormality in these patients. In this family, idiopathic atrial fibrillation seems to be transmitted as an autosomal dominant trait.