Myocardial acceleration during isovolumic contraction obtained from Doppler tissue imaging has been introduced as an index of right ventricular contractile function that is unaffected by the shape of the ventricle and loading conditions, but normal value of myocardial acceleration during isovolumic contraction and the effect of aging on the index are not known in normal fetuses. We studied 61 normal fetuses aged 20 to 39 weeks (29.8 ± 5.1 weeks). Fetuses were divided into 4 age groups: 20 to 24 weeks (n = 11); 25 to 29 weeks (n = 20); 30 to 34 weeks (n = 20); and 35 to 39 weeks (n = 10). Using Doppler tissue imaging, peak pre-ejection myocardial velocity was measured at the base of right ventricular free wall from 4-chamber view. Myocardial acceleration was calculated by dividing pre-ejection velocity by the time interval from onset of the pre-ejection myocardial velocity to the time at peak velocity of this wave. The mean pre-ejection myocardial velocity was 5.0 ± 1.1 cm/s. There was a stepwise increase in the pre-ejection myocardial velocity from the fetuses of 20 to 24 weeks to the fetuses of 35 to 39 weeks. The mean myocardial acceleration was 160 ± 30 cm/s². The mean myocardial acceleration did not differ between the fetuses aged 20 to 24 weeks (139 ± 13 cm/s²) and the fetuses aged 25 to 29 weeks (143 ± 21 cm/s²), but after 30 weeks increased with gestational age. For the total group combining the 4 different gestational age groups, the pre-ejection myocardial velocity and myocardial acceleration correlated with gestational age (r = 0.85 and 0.75). This study demonstrated the gestational age-related changes in pre-ejection myocardial velocity and myocardial acceleration. The load-independent index of contractility, myocardial acceleration, increased mainly after 30 weeks’ gestation.