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Fig. 6 Model of the synergistic and distinct roles of Nodal and FGF signaling in asymmetric cardiac morphogenesis. In the cardiac cone, Nodal promotes a left-lateralized migration to generate cardiac asymmetry, while FGF promotes a permissive migration in all CPCs. Nodal signaling also impinges on the actin cytoskeleton to promote F-actin asymmetry. Next, in the heart tube, both Nodal and FGF signals promote proper cardiac looping. Nodal promotes looping laterality to correctly position the chambers, while FGF induces the SHF which, in turn, is likely necessary for robust looping. The looped heart then matures to form a two-chambered heart by 48 hpf.