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Figure 4 nkx genes are required for maintenance of ventricular cardiomyocyte identity. Compared to the wild-type heart at 52 hpf (A), nkx2.5 mutants (B) exhibit a reduced ventricle and an enlarged atrium, with ectopic Amhc in some ventricular cells (arrows), and additional loss of a single allele of nkx2.7 (C) leads to increased presence of ectopic Amhc in the ventricle (arrows). nkx2.5;nkx2.7 double homozygotes (D) exhibit only a small ventricular remnant, with Amhc present throughout (arrow). Red fluorescence labels sarcomeric myosin heavy chain, and green fluorescence indicates localization of Amhc. Images adapted from [29].