In a total of 496 fetuses and newborns ranging in body weight from 60 to 5000 g, we performed a morphometric study of the vascular complex, that is the orifices of the great arterial trunks, ascending aorta, aortic arch, vessels branching from the aortic arch, the aortic isthmus, descending aorta, pulmonary trunk, orifices of the pulmonary arteries and arterial duct. In all, 17 different parameters were measured in each specimen, using several new parameters in addition to the measurements classically used in the aortic isthmus, arterial duct and pulmonary trunk. Anatomo-geometric models of these structures were developed, and stereometric formulas used to calculate the real volumes of the aortic isthmus, arterial duct and pulmonary trunk. The variations in the correlations between two measurable characteristics, that is, body weight and each of the morphometric parameters were analyzed, and the minimum, normal and maximum patterns of normality for each parameter were obtained with regression equations. The results show that the volume of the aortic isthmus increases by 0.03 ml for each millilitre increase in left ventricular volume. The isthmic volume increases by 0.32 ml for each millilitre increase in volume of the arterial duct and the volume of the pulmonary trunk increases by 6.4 ml for each increase of 1 millilitre in the volume of the aortic isthmus. The inner circumference of the aortic isthmus is greater than that of the arterial duct, whereas the former vessel is always shorter than the latter. We believe that these morphological data, when appropriately interpreted, have immediate clinical and surgical applications in the treatment of fetal and perinatal cardiovascular disorders.