In fetal life, the oval fossa valve (secondary to the atrial septum) is located on the left atrial side and is offset toward the left atrium to open the foramen ovale, which constitutes a normal right-to-left blood flow channel. Generally, the size of the foramen ovale is 4-6 mm, and greater than 6 mm means that the foramen ovale is enlarged, which may be related to factors such as small development of the foramen ovale, weak development of the foramen ovale, or ultrasound artifacts. In recent years, with the rise of fetal heart ultrasound, there are more “diagnoses” in the fetal period, but most of them are not clinically significant. The prognosis is generally good when the fetus is born with the closure of the foramen ovale and disappears, so it should not be induced. Very few of them can be maintained into adulthood and may be combined with atrial defect. In our hospital, we followed up 108 cases of fetal foramen ovale enlargement, only a few of them remained after birth. Health care measures: 1. No special treatment or care is needed during the fetal period; 2. Treatment: No treatment is required. Long-term prognosis: Complete normal life, study and work.