The purpose of this study was to evaluate color- and spectral Doppler ultrasound in the establishment of normal functional cardiovascular development features in the mouse fetus. Mouse fetuses (129Sv strain) were studied in utero between embryonic day (EDs) 9.5 and 19.5. Time-velocity curves were derived from Doppler interrogation of the aorta and umbilical artery. The sample volume was accurately placed on the vessels of interest based on color-Doppler images. From these curves, the following parameters were obtained: heart rate (HR), acceleration time (AT), and deceleration time (DT). HR increased between EDs 9.5 and 19.5 from 102.9 to 303.2 b.p.m. For the other parameters, the most significant change observed was the increase of DT in the umbilical artery at the end of pregnancy, corresponding to the appearance of a diastolic flow. We report the use of a commercially available, clinical, ultrasound unit to obtain quantitative data on the cardiovascular development in the mouse fetus. These results may be useful for the recognition of in utero cardiovascular dysfunction in transgenic or knock-out fetus.