Fetal cardiac biometry was conducted in the TM mode, after real time anatomical outlining of the plane of the four cardiac cavities, on 48 recordings of supposedly normal pregnancies of 23 to 39 weeks of amenorrhoea. Ten measurements were made for each patient, in an immediately subvalvular plane perpendicular to the septum (dimensions of the two ventricular cavities, of the wall of the two ventricles, and of the septum, in diastole and systole respectively). Functional results derived from this data showed that the difference between diastolic and systolic values for ventricular diameters increased with term, the ratio of the diastolic diameter of the right ventricle (RV) to that of the left ventricle (LV) was a constant: 1.23 +/- 0.12, and the size of the RV was always superior to that of the LV (+ + +). Alson noted was that percentage shortening of the LV was superior to that of the RV, and mean percentage thickenings of the RV and septum were inferior to that of the LV. A further observation was that interpretation of the kinetic of the septum requires precise knowledge of the plane of the section in relation to "the pivot point".