The genes that drive heart-cell differentiation in vertebrates and Drosophila are similar, even
though the Drosophila 'heart'is a simple tube and the vertebrate heart is a multichambered
physiologically complex organ. Mutational analysis in mice and, as particular focus of this
review, in zebrafish, reveals the additional genes brought into play to fashion these
evolutionarily 'new'organotypic components.