Abstract. BACKGROUND: In neonates without physiological pulmonary hypertension, left ventricular end-diastolic dimensions (LVDd) are determined with two-dimensional echocardiography and formulated equations. However, there has not been discussed the meanings of dimensions in early neonatal periods, although the short-axis view of the left ventricle is not round at this age. The objective of this study was to assess LVDd in neonates during early neonatal periods. METHODS: The study group consisted of 460 full-term neonates (230 boys; 230 girls) without congenital heart disease. The iE33 apparatus was employed to examine and measure the LVDds and the longest and shortest dimensions in the short-axis view. RESULTS: A significant difference was observed between the real LVDds and the estimated normal dimensions that were calculated from the formula; LVDd(mm) = 0.352×Ht(cm)+1.86, (P = 0.020). The mean LVDds were estimated to be 97% of the normal LVDds. The real LVDds were influenced by the angle formed by the real LVDds and the longest dimension. CONCLUSIONS: The real LVDds were shorter than normal LVDds. These findings establish normal values for LVDds in the early neonatal period.