Prkar1a KO (red text) causes reduction of cardiac-specific genes and a reduced number of cardiomyocytes with aberrant sarcomeres (Middle figure: white arrow: residual Z-disk; arrowhead: residual I-band)), eventually leading to a thin-walled, dilated heart (Right figure). At the end, these changes cause myxomagenesis (Left figure, arrows), and embryonic demise. These same pathways may be affected by knockout of other cardiac-specific transcription factors (blue text). A mechanism to account for myxomagenesis associated with mutation of MYH8 is also proposed in the same scheme. See text for details and references.