Introduction: The causative agent of Lyme disease is Borrelia Burgdoferi Gram-negative bacteria, belonging to the Spirochete family. Ixodes tick is the main trans-mission vector causing the disease in humans. The most commonly affected organs are the skin, joints and the nervous system, Lyme carditis being one of the rarest manifestations, with potentially lethal complications.

Objective: T he purpose of this case report is to dis-cuss the conduction disturbance associated to carditis as a unique manifestation of Lyme disease in the early disseminated phase encountered to a young patient with no history of cardiovascular disease.

Methods: 28 years old patient, without any cardiovas-cular antecedents neither any significant family medi-cal history, presents with a syncopal episode.

Results: The initial clinical examination reveals 37.2°C body temperature, heart rate of 35 bpm, arterial BP 110/50 mmHg. EKG: high degree transitory atrioven-tricular (AV) block and first degree AV block. Blood tests show leukocytosis with neutrophilia, erythrocy-te sedimentation rate 15mm/h, fibrinogen 455 mg/dl. Echocardiography shows no distended cardiac cavities with left ventricle preserved systolic and diastolic func-tions, EF 60%, and the presence of a filamentous lesion at the anterior mitral valve (AMV) level, which in the clinical context raised suspicion of infectious endocar-ditis. Transesophageal echocardiography is performed, which excludes the presence of vegetation or rupture of the AMV. Given the onset of an acute high degree AV block in a young patient, with no other suspected pathologies, a presumptive diagnosis of Lyme disease is made. Diagnosis is confirmed by positive anti Bore-lia Burgodoferi IgM, and Western Blot test also posi-tive (with the presence of anti Borelia Burgdoferi IgM antibodies). Treated initially with Ceftriaxone and afterwards with Doxycycline, the complete remission of the AV block was observed and confirmed by several Holter monitor recordings.

Conclusions: Lyme carditis is one of the rarest mani-festations of Lyme disease, but it has an important sig-nificance in the differential diagnosis in youth’s atrio-ventricular block. Although it is potentially severe, the cardiac damage is completely reversible after the dia-gnosis followed by the adequate etiological treatment.