Congenital heart block (CHB), a life-threatening manifestation of neonatal lupus, offers aunique opportunity to study the effect or arm of immunity and define the pathogenicity of an autoantibody in mediating tissue injury. This review focuses on our recent in vitro model which supports a cascade from antibody insult to unchecked fibrosis. In brief, it is proposed that the fetal cardiac myocyte undergoes apoptosis which facilitates transfer of intracellular Ro and La antigens to the surface where they are bound by circulating maternal autoantibodies (anti-SSA/Ro-SSB/La antibodies). Scavenging macrophages phagocytose these inadvertently "opsonized" cardiocytes, leading to the secretion of pro-inflammatory and pro-fibrotic cytokines, the latter of which transdifferentiate fibroblasts into myofibroblasts and thereby promote scarring. Immunohistologic study of a heart from a neonate dying of CHB supports this model in that macrophages and myofibroblasts were demonstrated. To facilitate both basic and clinical research, a Research Registry for Neonatal Lupus was established in 1994 by the U.S. National Institute of Arthritis, Musculoskeletal and Skin Diseases. Maternal and fetal outcomes are addressed as well as recurrence rates. Laboratory evaluation and management decisions during pregnancy are provided.