A vocabulary describing heart development constructed using literature references. The format of the vocabulary and other vocabularies in this manuscript is as follows: Indentation reflects parent–child relationships; the < symbol indicates that the child is a part of its parent; and the % symbol indicates that the child is a type of its parent. Multiple parentage is indicated by two terms on the same line, where the first term is a child of the second term. The colored portion of the graph corresponds to the similarly colored diagram in the schematic shown in Figure 6.