The human coronary sinus is an evolutionary modification of the terminal part of the left sinus horn. Anatomically, the coronary sinus is a short, broad vessel that runs along the coronary groove situated on the diaphragmatic surface of the heart. This structure, which opens into the right atrium, collects blood from the great cardiac vein and from other veins of the heart as well. In this study, we assessed the growth and dimensions of the coronary sinus at the fourth and eighth months of fetal development from whole material received from the Nicolaus Copernicus University, Collegium Medicum, Department of Histology and Embryology in Bydgoszcz. A group of 219 specimens, 105 male and 114 female fetuses, presented no visible malformations or developmental abnormalities. The results of this study determined that the dimension of the coronary sinus during prenatal development is not sexually dimorphic. Furthermore, following a monthly period of rapid growth in length of this structure, there are no further increases in length after the six months gestation. Finally, we concluded that the dimensions of the coronary sinus obtained during autopsy are similar to those determined through intravital ultrasound examination. The diameter of the coronary sinus is the best parameter to monitoring the fetal age and the growing of the fetus. Accordingly, we suggest that the best way of estimate for proper blood drainage from heart veins is study of coronary sinus volume.