Lyme disease is caused by Borrelia burgdorferi spirochetes which are transmitted by ticks. Despite the development of many monitoring and prevention programs, the disease is still the most often diagnosed tick-borne infection in humans and animals in the Northern Hemisphere. Late diagnosis and improperly treated, borreliosis can result in serious damage to internal organs. Recently, the number of Lyme disease cases in dogs, has significantly increased. Cardiac manifestations become frequently recognized in early disseminated phase of the disease. According to the current opinions, a serious complication is Lyme carditis, a common manifestation, considered as one of the main causes of fatalities in humans. The aim of this paper was to present a clinical case of Lyme carditis in a four year old Bavarian mountain dog