P>Objective To explore the relationship between migrating neural crest cells expressing cellular retinoic acid binding protein 1(CRABP1) and islet 1（ISL-1）positive cardiac progenitor cells and the development of the outflow tract (OFT) of the mouse embryonic heart. Methods Serial sections of thirty-six mouse embryonic hearts from embryonic 8.5 days (E8.5d) to E13d were stained immunohistochemically or immunofluorescently with antibodies against α-smooth muscle actin (α-SMA), myosin heavy chain (MHC), ISL-1, CRABP1 and phosphorylated histone H3 (PHH3). Results From E8.5d to E10d, ISL-1 positive cardiac progenitor cells were sequentially detected in the mesenchyme of the dorsal mesocardium, the mesenchyme surrounding the primary pharynx, the craniofacial mesenchyme and core mesenchyme in the branchial arches as well as the splanchnic mesoderm dorsal to the pericardial cavity that constituted second heart field (SHF) for the development of OFT of heart tube. From E11d to E13d, ISL-1 positive cells ventral to the pharynx formed a cone-shaped structure from which ISL-1 positive cells extended towards the developing intrapericardial aorta, pulmonary trunk and aorto-pulmonary septum (AP septum). CRABP1 positive neural crest cells were interspersed among the ISL-1 positive cells at early stages. A few CRABP1 and ISL-1 double-positive cells were found at the distal pole of the OFT. At E10d, CRABP1 positive cells were uniquely distributed surrounding the ISL-1 positive core mesenchyme in branchial arches. Thereafter, the gradual disappearance of CRABP1 expression in the wall of aortic arch and other regions was followed by expression of α-SMA. Conclusion The ISL-1 positive SHF is a dynamic structure where myocardial cells are gradually added to the arterial pole of the heart tube under the cooperation of neural crest cells during E8.d-10d.After E11d, SHF is involved in the development of the smooth muscle cells in the wall