Conal myocardium and mesenchymal remodelling.

Adjacent cephalo-caudal sections of the embryonic heart from stages 22HH to 26HH. (A) Stage 22HH. The lumen of the conus and the AV canal are side by side. (A’) Immunolocalization of the skeletal muscle myosin (green). Observe the tubular structure of the conal myocardium, the homogeneously distributed mesenchymal tissue (Mes), and the endocardium (red nucleus). (B, B’) Stage 24HH. The conus is in a slightly left and ventral position with respect to the AV canal. (B’). A small myocardial notch (*) is observed at the left-dorsal conal wall. (C, C’). Stage 26HH. Observe the loss of continuity at the thinned left-dorsal myocardial conal wall (*) and the incipient endocardial conal crest (X). Abbreviations: AVC = atrioventricular canal; Mes = mesenchymal tissue.