Interventricular septal dissection (IVSD) is a critical condition characterized by the separation of the intraventricular septum into two layers, forming an intermediate layer with a cystic cavity that communicates with the root of the aorta or ventricle，with extremely low morbidity and high mortality. our study presented a very rare fetal case of IVSD after acute inferior myocardial infarction(MI) , exploring the etiology and pathogenesis of the disease, the key points and the clinical value of ultrasound diagnosis.