Type Ⅲ redundancy of the foramen ovale flap (RFOF) mimics hemodynamic changes of mitral stenosis(MS), which has not been particularly highlighted in previous literature. This type of MS carries a favorable prognosis.

Previous studies have shown that Type Ⅲ redundancy of the foramen ovale flap (RFOF) can mimic the hemodynamic features of other congenital heart diseases (CHD), potentially causing misdiagnosis during the fetal period. In this study, we present two cases of Type Ⅲ RFOF in fetuses, which can mimic mitral stenosis (MS). This manifestation has not been particularly highlighted in previous literature. However, this type of MS carries a favorable prognosis.