BACKGROUND Infections caused by tick-borne pathogens such as Bartonella spp., Borrelia burgdorferi s.l., Coxiella burnetii, and Rickettsia spp. are capable of causing serious lesions of the mitral and aortic valves, leading to a need for valve replacement. OBJECTIVES The aim of the study was to determine whether such cases are sporadic or frequent. An additional goal was to establish effective diagnostic methods to detect these infections. MATERIAL AND METHODS The study involved 148 patients undergoing valve replacement. Blood samples were drawn for serological testing. Samples of the removed mitral and aortic valves were tested with polymerase chain reaction and immunohistochemical staining. RESULTS Specific antibodies to Bartonella spp. were detected in 47 patients (31.7%) and in 1 of the healthy controls (1%) (p < 0.05). Antibodies to B. burgdorferi spirochetes were found in 18 of the patients (12.2%) and in 6 blood donors from the control group (5.8%) (p < 0.1). Antibodies to Rickettsia spp. were detected in 12 (8.1%) and to C. burnetii phase I and II antigens in the serum of 1 patient. All the participants in the control group were seronegative to C. burnetii and Rickettsia spp. antigens. Polymerase chain reaction (PCR) tests for detection of Bartonella spp., B. burgdorferi s.l., C. burnetii and Rickettsia spp. DNA in the valve samples were all negative. Inflammation foci with mononuclear lymphoid cells in the aortic and mitral valves were seen in sections stained with hematoxiline and eozine. In sections dyed using the indirect immunofluorescence method with hyperimmune sera, Bartonella spp. and Rickettsia spp. were found. CONCLUSIONS The results obtained indicate that laboratory diagnostics for patients with heart disorders should be expanded to include tests detecting tick-borne zoonoses such as bartonelloses, Lyme borreliosis, rickettsioses and Q fever.