OBJECTIVES:Color M-mode propagation velocity (Vp) is a measure of diastolic function in adults and, when combined with early diastolic inflow velocity (E), the ratio E/Vp reflects ventricular filling pressure. Early detection of diastolic compromise may benefit fetal patients at risk for developing heart failure. The objectives of this study were to measure values for Vp and inflow peak E in a group of normal fetuses, to analyze age-dependent alterations in these measurements, and to evaluate the interobserver and intraobserver variability of the measurements. METHODS:Thirty-two normal fetuses at between 20 and 35 weeks' gestation underwent echocardiography. Color M-mode Vp was measured from the four-chamber view for the right (RV) and left (LV) ventricles, and mitral and tricuspid inflow velocities were determined by pulsed-wave Doppler ultrasound. The values obtained were compared with previously reported findings in adults. RESULTS:Adequate tracings were obtainable in 23 patients for the RV and 29 for the LV. Mean Vp values for the RV (15.3 +/- 3.2 cm/s) and LV (20.8 +/- 5.6 cm/s) were lower than normal adult values, and Vp values were significantly lower for the RV than the LV (P < 0.001). Applying Bazett's heart rate correction, values for RV (23.4 +/- 4.8 cm/s) and LV (31.9 +/- 8.7 cm/s) remained lower than normal adult values. There was a linear correlation of Vp with gestational age for the RV (R = 0.69, P < 0.001), and the ratio of E/Vp corrected for heart rate for the RV (1.51 +/- 0.26) remained constant throughout gestation. Interobserver bias was high but intraobserver bias low, at 19 and 1.1%, respectively. CONCLUSIONS:Vp is lower in fetal than in adult life. Vp for the RV changes in a manner indicative of improving diastolic function throughout normal gestation, providing insight into the alterations in diastolic function with gestation that contribute to increases in cardiac output. The use of Vp to assess diastolic function disturbance in fetuses is feasible, but high interobserver variability is problematic.