The authors present the case of a 44-year-old patient who was admitted to the hospital because of AV block of degree III. Six weeks earlier a tick was removed from the left foot of the patient. Two weeks later an erythema of 8 cm in diameter, spreading peripherally as well as painful inguinal lymphadenitis developed at the site of the bite with transient arthralgia and myalgia in the region of the waist and left lower limb. After the temporary use of pacemaker, steroid and atropine therapy applied because of the pronounced bradycardia the block became of degree I on the 4th day however negative T-waves appeared in leads III, aVF, V3. By the 14th day the AV time returned to normal and the pathological signs of repolarization disappeared. Serological examinations revealed increased Borrelia burgdorferi antibody level. Lyme's carditis may be prevented by starting the antibiotic therapy at the time of the chronic erythema migrans. Upon medication the patient may recover from the carditis without remaining symptoms.