105 North American and European cases of Lyme carditis, being documented and in part published in the period 1977-1990, are reviewed and compared. The male: female ratio was 3:1, as well in Europe as in the USA. Transient atrioventricular block is the most frequent manifestation of Lyme carditis, with a remarkable similarity in the frequency of complete AV block and attending neurological illness in Europe and the USA. The distribution of (maximal observed) atrioventricular block in all patients existed of 49% third degree, 16% second degree and 12% first degree. Data of electrophysiological studies show that affection of the cardiac conduction system can be local or very diffuse. Other manifestations like rhythm disturbances, (myo)pericarditis and heart failure were less striking and have a less similar frequency in the European and American cases. Medicational therapy seems not to be an unconditional requirement for recovery of Lyme carditis itself, but cannot be withheld because of the proven beneficial effects of antibiotic therapy in other manifestations of Lyme borreliosis. Temporary pacemakers are frequently inserted, but pacemaker implantation is rarely needed. The overall prognosis of Lyme carditis seems to be good, although delayed recovery has been described and possible late manifestations have been suggested.