Current understanding of organ-level vertebrate heart development has been gained primarily from studies of avian and amphibian heart development from whole-mount culture studies and subsequent dissections and serial sections of the heart during different stages of development of the organism. Chick embryos have been particularly accessible for experimental manipulation and functional analyses as compared with normal mouse embryonic hearts, which are poorly accessible without disturbing the placental blood flow. Specifically, in the study of vertebrate heart development, there has been a lack of noninvasive techniques for physiologic assessment of mouse cardiac function. There have been several studies describing hemodynamic changes in the developing chick embryonic heart using Doppler techniques (1 –4 ). Most of these studies have been invasive in nature such that the hemodynamic status may be disturbed.
