Lyme borreliosis is a worldwide tick-borne illness caused by the spirochete Borrelia burgdorferi sensu lato. The number of cases rises every year. The disease progresses with an unpredictable course and affects various organ systems. Early stage skin rash, erythema migrans, and later neurologic, cardiac, and musculoskeletal involvement are distinctive of manifest infection. The most accurate for diagnosis and the most common clinical sign of the disease is erythema migrans. During the course of the disease, the heart is also involved. The principal clinical signs are conduction disturbances, myopericarditis, and cardiomyopathies. If diagnosed early, electrocardiographic changes may influence the choice of antibiotic treatment and progno­sis. Electrocardiographic changes were studied in children with erythema migrans and compared to electrocardiographic findings from a comparable healthy control group. 147 children with typical erythema migrans were included in our prospective study. The con­trol group consisted of 148 healthy children of the same sex and comparable age. Electrocardiographs were obtained for patients and for the control group. All children were divided into age groups according to their heart rate, PR interval duration, heart axis, dura­tion and amplitude of the QRS interval, Q wave, R/S ratio, T wave and QT interval. Statistical data were processed using the s-test, t-test (Kruskal-Wallis) and χ² test (Fischer). 5% of patients and 14% of healthy children from the control group had pathological elec­trocardiographs. In comparison with healthy children, the patients had shorter PR and RR interval durations and lower R and S wave voltage in V₁. Among the patients, boys had patho­logical electrocardiographs more often than girls. Patients with multiple erythema migrans did not have more frequent pathologic electrocardiographs than patients with solitary ery­thema migrans. Patients with associated complaints, patients with Borrelia burgdorferi sensu lato isolated from blood and patients with meningitis also frequently lacked pathologic elec­trocardiographs. It was concluded from the results that in children with erythema migrans pathologic electrocardiographs are not more frequent than in the group of healthy children of the same sex and comparable age. In case of progressive Lyme borreliosis, the typical clin­ical signs and symptoms are not understood as risk factors of more frequent pathologic electrocardiographic findings in patients with erythema migrans.