After one day of dizziness a 28-year-old man experienced a syncope on getting up. ECG revealed a 3 degrees atrioventricular (AV) block unresponsive to drug treatment. A temporary pacemaker was implanted. Erythema migrans 4 weeks before admission suggested Lyme carditis, and the diagnosis was confirmed serologically (ELISA increased polyvalently, IgM antibody titre 1:64, IgG antibody titre 1:512). On antibiotic treatment with amoxicillin (1 g three times daily) and prednisolone (initially 80 mg daily, with gradual dose reduction) the sinuatrial block regressed within 10 days. Holter monitoring still demonstrated occasional sinoatrial conduction disturbances for some days, until sinus rhythm was permanently re-established. This case illustrates that transitory AV block can be the sole manifestation of sporadic Lyme disease in Europe and should therefore be included in the differential diagnosis of any acute cardiac disease.