Recent advances in 3D printing allow the generation of tissue models that provide a unique in vitro platform to recapitulate and analyze complex cardiovascular anatomies, including the developing human heart. While it is challenging to quantify the 3D blood flow dynamics in the developing fetal heart, with spatial resolution on the order of a millimeter or less, printed tissue constructs allow such 3D measurements by reconstructing multiple 2D measurements under constant flow conditions. Such functional phantoms can offer critical insights into hemodynamics in healthy and diseased states, including complicated flow conditions in congenital heart defects during the early stage of prenatal development. In this study, ultrasound-compatible tissue-mimicking phantoms were fabricated using water-soluble 3D printed fetal human heart models, i.e., an embryonic heart tube at day 22 and a fetal left ventricle at week 33 after fertilization. An ultrasound-based 3D velocimetry method was used to measure the flow velocity magnitude and direction in these anatomically-accurate phantom models of the linear heart tube and the left ventricle.