目的 探讨小鼠胚胎心脏房室管分隔、重塑过程中房室管心肌与心外膜的变化规律。 方法 选用抗心肌肌球蛋白轻链Ⅱa（MLC2a）抗体、抗心肌肌球蛋白轻链Ⅱ（MLC-2）抗体、抗转录因子Tbx3（Tbx3）抗体、抗淋巴增强因子1（Lef1）抗体，对25只胚龄10～15 d 小鼠胚胎切片进行免疫组织化学和免疫荧光染色。结果 胚龄10～15 d，房室管心肌呈MLC2a阳性、MLC-2阴性，同时表达Tbx3。胚龄11～12 d，心外膜形成。胚龄12～13 d，两侧房室管心内膜垫彼此接近并融合形成房室瓣，心外膜来源间充质细胞数量增加，部分表达Lef1。胚龄13 d开始，部分心外膜来源间充质细胞穿过心肌延伸入壁侧房室瓣。胚龄15 d，房室瓣膜基部直接与MLC2a阳性的房室管心肌相连。 结论 小鼠胚胎房室管心肌发育为成体心脏房室环瓣膜基部的心肌；心外膜通过产生间充质细胞参与房室瓣的形成。

Objective To investigate the morphological characteristics of the myocardium and epicardium during the septation and remodeling of the atrioventricular canal in the mouse embryonic heart. Methods Serial sections of twenty-five mouse embryos during embryonic day(ED) 10 to ED15 were stained by immunohistochemistry and immunofluorescence with antibodies against myosin light chain 2a (MLC2a), myosin regulatory light chain 2 (MLC-2), T-box transcription factor 3 (Tbx3), and Lymphoid enhancer-binding factor 1 (Lef1). Results Immunohistochemistry and immunofluorescent staining for MLC2a and Tbx3 were positive in the atrioventricular canal myocardium of ED10 to ED15 mice, but for MLC2 was negative. During ED11 to ED12, the epicardium was observed. At ED12 and ED13, the bilateral atrioventricular canal cushions began to fuse with each other and formed the atrioventricular valve. The epicardium derived mesenchymal cells between the atrioventricular myocardium and epicardium were increased, part of which showed the Lef1 immunohistochemistry positive staining. From ED13, some epicardial cells derived from mesenchymal cells transversed through the myocardium to parietal atrioventricular valve. At ED15, the base of the atrioventricular valve was directly connected with the MLC2a positive atrioventricular myocardium. Conclusion The atrioventricular myocardium develops into the myocardium to support the base of the valves of the adult atrioventricular ring. The epicardium provides mesenchymal cells which contribute to the formation of atrioventricular valves.