Third degree atrioventricular (AV) heart block with severe Adams-Stokes attacks in 3 patients with Lyme borreliosis is described. All patients had similar clinical manifestations: previously healthy, they experience syncope as an abrupt onset of the disease. Data on skin changes--erythema migrans--was subsequently obtained, although the patients did not recall being bitten by a tick. Diagnoses were based on clinical manifestations and on positive serologic test results to borrelia. Following AV block returned to sinus rhythm with normal AV conduction in all patients.