Lyme disease, due to infection with Borrelia burgdorferi transmitted by ticks, is most frequently manifested by arthritis and neurological complications. In approximately 8% of cases, however, carditis, usually reflected in AV block, is the leading symptom. The case histories of 2 males and 1 female aged 23 to 37 years with AV block caused by Borrelia burgdorferi are presented. Main symptoms were exertional dyspnea, palpitations, dizziness and syncope. One patient was treated with diclofenac and two with penicillin. The course was uniformally benign and cardiac abnormalities disappeared within 1-3 weeks.