ObjectiveTo ascertain the clinical significance of right fetal cardiac axis.MethodsFetal cardiac axis was assessed prospectively in ultrasound examinations of 16,562 fetuses over a 6-year period.ResultsTwenty-two fetuses had a right cardiac axis. When classified by ventricular and atrial configuration, six fetuses had mirror-image hearts with situs inversus, 12 had rotation of the heart axis alone, and four had inversion of the ventricles. Fourteen of the 22 had underlying structural cardiac defects, most of which were atrioventricular septal defects, double outlet right ventricles, or common atria. The chromosomes and/or phenotypes of all 22 were normal. All four fetuses with polysplenia and asplenia died. Major extracardiac defects were few (two) but lethal.ConclusionRight cardiac axis in the fetus is associated with a high incidence of structural cardiac defects. In the absence of severe extracardiac defects, polysplenia, or asplenia, neonatal outcome was good.