Fetal pulmonary venous flow pattern is determined by left atrial pressure: report of two cases of left heart hypoplasia, one with patent and the other with closed interatrial communication.

We report two cases of fetal left heart hypoplasia with extremes of size of interatrial communication, i.e. a closed foramen ovale and an atrial septal defect. Doppler examinations of the pulmonary veins showed almost to and fro flow in the fetus with the closed foramen ovale and, in contrast, a normal flow velocity waveform in the fetus with the atrial septal defect, despite mitral atresia. Our observations support the importance of left atrial pressure in the creation of a pulmonary venous flow pattern in the fetus.