The heart of an anencephalic baby can be used as a donor after death. There exists insufficient information in literature, however, for the possible morphological differences in anencephalic hearts. This study compares ventricular myocardial thicknesses of anencephalic fetuses with normal fetuses in the same gestational age group. The comparison was made histologically on the slices taken from three levels of anterior and posterior walls of the left and right ventricles and from two levels of the interventricular septum. When each level was taken into account separately, the middle part of the left ventricular anterior wall was detected thinner in anencephalics (P = 0.010). When the mean value for each wall (anterior and posterior) was taken into account, left ventricular anterior wall was found thinner in anencephalics (P = 0.005). When the mean value for each ventricle was compared, the left ventricular wall was detected thinner in anencephalics (P = 0.025). These results support the idea that absence of the cerebral cortex results in modifications of the fetal heart. Because differences were limited to the left ventricular anterior wall non-homogenously, factors other than the decrease in the heart load (e.g., changes in intrathoracic anatomy) might also affect the myocardial features. When the mean value of right ventricle was compared to the left within the normal and anencephalic groups separately, the left ventricle was thicker than the right in normal fetuses (P = 0.016). In anencephalics the difference between two ventricular walls was insignificant (P = 0.084). This supports the left ventricular dominance in normal fetuses but not in anencephalics for the 27-34 weeks of age group. We suggest that when an anencephalic heart is intended to use as a donor, possible alterations presented in this article should be taken into account. (C) 2004 Wiley-Liss, Inc.