In the series of 91 samples of human heart obtained from fetuses at developmental weeks 17–28 and formed without major defects and minor anomalies, the relief of the sinus part (SP) of the interventricular septum (IVS) was studied on the side of right ventricle (RV). Myocardial trabeculae carneae (MTC) were found in SP in 96.7% of the cases. MTC, associated with the IVS myocardium along their entire length (parietal MTC), were twice as frequent as bridge-like MTC. MTC were predominantly concentrated at the posterior corner of the RV; these were exclusively bridge-like MTC. Most frequently, MTC were absent near the IVS membranous region. An individual anatomical variability of the relief of the RV in the fetal heart was demonstrated. Depending on the number, anatomical type and mutual position of the MTC, three variants of the SP relief were distinguished: hypertrabecular, hypotrabecular and intermediate. From week 17 to week 28 of the intrauterine life, the hearts of the fetuses may differ in the form of MTC, however their number and the anatomical type within a particular variant of the SP remained constant The existence of the parietal longitudinal MTC on the right side of the IVS SP is proposed to be one of the hallmarks of the anatomically «normal» (ordinarily formed) heart in the human fetuses.