The relatively low percent of patients affected with the cardiac form of Lyme borreliosis is difficult to diagnose, especially if the disease manifests itself in ways other than atrio-ventricular blockade. The advanced stage of Lyme carditis manifesting as dilated cardiomyopathy is a special case of this affliction. The authors of this report present clinical experience with an attempt to support the working hypothesis about involvement of Lyme borreliosis infection in the development of dilated cardiomyopathy. The patients were clinically examined thoroughly with special attention to the cardiovascular system. In addition to the basic clinical methods, the following procedures have been employed: dynamic Holter's electrocardiography, exercise ECG test, coronarography, and myocardial biopsy. From laboratory methods pertaining to the detection of Borrelia, ELISA method, Western blot, PCR, electron microscopy and histopathological analysis were used. In all three cases, clinical and laboratory findings provided the evidence of the borreliosis infection involvement in the development of dilated cardiomyopathy.