Non-compaction can be identified in the fetus. Fetal non-compaction most often involves the left ventricle, but can involve the right ventricle or both ventricles. The myocardial ultrastructure of fetal ventricular non-compaction has certain unique characteristics regarding the maturation of the mitochondria, sarcomeres, and myocardial fibers. © 2014 John Wiley & Sons, Ltd.