Lyme disease is a systemic illness with skin, neurologic, joint, and cardiac involvement. Absence of typical skin lesion--erythema chronicum migrans--during the first period of disease may cause the diagnosis difficult. Syncope due to complete atrioventricular block was the first symptom of disease in our patient, but no tick bite anamnestic data were available. Quick changes on EKG tracing during cardiac pacing were present. Echocardiography revealed left ventricular dysfunction. Specific immunological tests confirmed the diagnostic suspicion. Cardiac pacing, digitalis and antibiotic treatment ensued in complete recovery. No other systemic lesion appeared. Lyme carditis may be the only manifestation of the disease. Temporary cardiac pacing may be necessary.