Schematic representation of maternal antibodies interaction with cardiac Ca channels. The acute events are initiated by binding of the circulating maternal antibodies to surface L-type Ca channels. This leads to cross-linking the antibody-antigen complexes (step 1). As a result of the interaction, the surface complex is internalized and degraded by lysozymes (step 2). In step 3 and 3a, two scenarios are proposed: fetal cells with enough remaining Ca channels will survive (fetal discordance of twins) and secure atrioventricular conduction; those with severe depletion of Ca channels (step 4) will result in Ca dysregulation and apoptosis (step 5). This may lead to the translocation of the intracellular SSA/Ro and SSB/La to the cell surface to bind to their cognate antibodies (step 5). Altogether, this process will eventually trigger inflammation (step 6), cell death, fibrosis and calcification (see text for more details).