The study investigates the role of the transcription factor MEF2C in mouse cardiac morphogenesis and myogenesis. MEF2C, a member of the MADS-box transcription factor family, is expressed in heart precursor cells before the formation of the linear heart tube. In homozygous null mutants of *MEF2C*, the heart tube fails to loop, the future right ventricle does not form, and a subset of cardiac muscle genes are not expressed. The absence of the right ventricular region in mutant hearts correlates with down-regulation of the *dHAND* gene, which is essential for cardiac morphogenesis. These findings indicate that MEF2C is crucial for cardiac myogenesis and right ventricular development. The study also reveals that MEF2C regulates the expression of specific cardiac genes and may control the activity of regionally restricted regulatory factors, such as dHAND, during right ventricular development.The study investigates the role of the transcription factor MEF2C in mouse cardiac morphogenesis and myogenesis. MEF2C, a member of the MADS-box transcription factor family, is expressed in heart precursor cells before the formation of the linear heart tube. In homozygous null mutants of *MEF2C*, the heart tube fails to loop, the future right ventricle does not form, and a subset of cardiac muscle genes are not expressed. The absence of the right ventricular region in mutant hearts correlates with down-regulation of the *dHAND* gene, which is essential for cardiac morphogenesis. These findings indicate that MEF2C is crucial for cardiac myogenesis and right ventricular development. The study also reveals that MEF2C regulates the expression of specific cardiac genes and may control the activity of regionally restricted regulatory factors, such as dHAND, during right ventricular development.