The third degree A-V heart block with severe Adams-Stokes attacks in nine patients with Lyme borreliosis was described. All patients had similar clinical picture: previously healthy with syncope as abrupt onset of the disease. Data on skin changes--erythema migrans--were obtained subsequently although the patients did not recall being bitten by a tick. Diagnosis was based on clinical manifestation, and on positive serologic tests to Borrelia. After the administered therapy (on admission atropine 0.5 mg i.v., and/or isoproterenol 0.02 mcg/kg/min, temporary pace-maker in two patients; and after proved diagnosis penicillin 20 mil. unit per day 10 days, and tetracyclin 2.0 gr per day 20 days A-V block returned to sinus rhythm with normal A-V conduction, and all biochemical parameters returned to normal limits. Perimyocarditis is not rare during Lyme borreliosis, but in this case infection syndrome is dominant.