The parallel arrangement of the fetal intracardiac circulation requires unrestricted flow of blood through the foramen ovale in the atrial septum. Restriction to this flow is a significant cardiac abnormality, with potentially serious sequelae in post-natal life. A wide spectrum of abnormalities has been associated to the restriction of flow through the foramen ovale, including enlargement of right atrium, hypertrophy of right ventricle, enlargement of tricuspid valve annulus, hypoplastic syndrome of left heart, non-immune hydrops fetalis and supraventricular tachycardias. We report the diagnosis and follow-up of a fetus identified in the prenatal period, in whom the restriction of the foramen ovale originated severe tricuspid regurgitation and severe right ventricular hypocontractility, despite the morphologically normal tricuspid valve. After delivery, there was complete resolution of the clinical findings. The paramount importance of complete assessment of interatrial flow in high risk fetuses, allowing for the early detection and intervention, is emphasized.