Fetal ductal constriction (DC) can depress right ventricular (RV) function. However, noninvasive assessment of fetal RV function remains difficult. We evaluated RV and left ventricular (LV) performance in fetuses with DC using the Doppler-derived Tei index. The Tei index measures the ratio of total time spent in isovolumic contraction and relaxation (isovolumic time) to the ejection time. Tricuspid inflow and RV outflow Doppler traces for the derivation of RV Tei indexes and mitral inflow and LV outflow traces for LV Tei indexes were measured in 78 fetuses of pregnant women who received indomethacin and 70 normal fetuses (gestational ages ranging from 20 to 39 weeks). DC occurred in 23 fetuses, defined as pulsatility index <1.9. In fetuses with DC, the RV isovolumic time was prolonged and RV ejection time was shortened, and the RV Tei index was high compared with those in fetuses that received indomethacin without DC and normal fetuses. Also, the RV Tei index clearly separated the fetuses with DC from normal and fetuses that received indomethacin without DC (0.74 +/- 0.14 vs 0.35 +/- 0.07 and 0.37 +/- 0.06, respectively; p <0.0001). The LV Tei index was not affected by DC. Serial study in 7 fetuses with DC showed that the RV Tei index decreased from 0.69 +/- 0.12 to 0.38 +/- 0.04 (p = 0.0002) after discontinuation of indomethacin coincident with ductal relaxation, although it remained elevated in 2 cases at the time of ductal relaxation. Thus, the Tei index is a useful and sensitive indicator for detecting abnormal RV performance in fetuses with DC.