Fig. 1.

Schematic presentation of the stages of heart development. Beginning from the blastocyst and ending with a functioning organ (heart), the embryo’s complexity increases substantially. Starting from the undifferentiated cells, the embryo begins to form via a series of coordinated migratory patterns and rearrangements of the cells establishing physical boundaries and the formation of the three germ layers: endoderm, ectoderm, and mesoderm. The complexity increases as the differentiation of the cells (both spatial and phenotypical) progresses establishing the orientation of the embryo (e.g., anterior vs. posterior), the location of future organs, the matrix, and the beginning of the vascular network. Mechanical loading also increases in complexity during organogenesis, leading to a completely competent and functioning heart.