SummaryTissue Doppler velocity during early diastole (e') is one of the most feasible and reproducible echocardiographic assessments to reflect active relaxation of the left ventricle. Although several reports have described the mechanisms of temporal diastolic dysfunction in the early neonatal period, factors influencing diastolic function have not been determined. The purpose of this study was to elucidate factors significantly influencing e' in the early neonatal period.A total of 179 consecutive normal neonates underwent echocardiographic studies performed at 0 days and 5-10 days after birth. The statistical relationships between e' and age, body weight, mean blood pressure, heart rate, shortening fraction of the left ventricle, peak systolic motion velocity (s'), early diastolic transmitral flow velocity over annulus velocity, Tei index, and diastolic wall strain (DWS) were analyzed.Between the 0 days and 5-10-days-after birth groups, significant differences were shown in mean blood pressure, shortening fraction of left ventricle, e', and Tei index. Age, body weight, mean blood pressure, s', and DWS showed significant correlations with e'. In multivariate regression analysis within these parameters, s' (β = 0.6119, P < 0.0001) and DWS (β = 0.1216, P = 0.0321) showed positive correlations with e'.Longitudinal systolic motion velocity and ventricular wall stiffness of the left ventricle influence diastolic relaxation in normal neonates. Age, body weight, and circumferential systolic function are not significant factors.(Int Heart J 2018; 59: 149-153) Key words: Diastolic wall strain, Diastolic function, Myocardial stiffness T issue Doppler velocity during early diastole (e') is one of the echocardiographic parameters reflecting ventricular relaxation. This feasible and noninvasive assessment can evaluate direct myocardial diastolic function reproducibly. Neonates are known to show temporary diastolic dysfunction soon after birth, but the mechanisms underlying this dysfunction are not clearly identified. In a previous study, the effects of afterload and right ventricular pressure overload due to physiological pulmonary hypertension, maturation, and the number of myocytes was inferred as one factor related to the diastolic function of neonates in the early period.1-4) Including such factors, significant hemodynamic changes occur during the transition from the fetal to the neonatal environment, and these changes could be presented as characteristic in the neonatal period. Besides these hemodynamic and pathological factors, individual background characteristics such as age, body weight at birth, and systolic function should be considered to have potential relationships with diastolic function. The relationships among these various factors are being considered, but the mechanisms underlying the development and maturation of diastolic function in normal neonates have yet to be clarified. The purpose of this study was thus to investigate the factors influencing e', the representative parameter for ventricular relaxa...