Lyme carditis is typically characterized by varying degrees of intermittent atrioventricular block occurring within weeks of infection with Borrelia burgdorferi. Myocarditis and/or pericarditis may occur. Cardiomyopathy has been associated with B. burgdorferi in Europe, but not in the United States. Patients with unexplained atrioventricular block or myopericarditis should be questioned for recent travel to tick-endemic areas, and for a history of erythema migrans rash, "viral-like" illness, aseptic meningitis, cranial nerve palsy, radiculitis, or oligoarthritis. However, the absence of a recognized tick bite or rash does not rule out Lyme disease. The diagnosis of Lyme carditis should be supported by the presence of concurrent erythema migrans, or by positive results of 2-step laboratory testing for antibodies to B. burgdorferi. False positive results may occur, emphasizing the importance of clinical judgment in attributing specific manifestations to B. burgdorferi infection. Carditis generally resolves spontaneously, but antimicrobial therapy can shorten symptom duration and prevent potential cardiac and non-cardiac sequelae. Cardiac manifestations generally resolve spontaneously, but antimicrobial therapy can shorten symptom duration and prevent potential cardiac and non-cardiac sequelae. The prognosis for Lyme carditis is excellent.