We report two children with acquired third degree AV-block caused by acute myocarditis. The diagnosis was proven by endomyocardial biopsy. Severe lymphocytic myocardial infiltration was shown using immunohistological methods. One of the children was treated with prednisone During therapy conduction disturbance nearly disappeared and infiltration was markedly reduced in a subsequent biopsy. In the other patient the parents refused immunosuppressive treatment and a permanent pacemaker was necessary for persistent bradycardia.
Conclusion: Immunohistological staining of an endomyocardial biopsy can be used to establish the diagnosis of myocarditis in patients with atypical clinical manifestation, such as complete AV-block, and can support the decision for therapy. In one patient improvement was documented by the disappearance of inflammatory activity in a repeated biopsy.