The vertebrate heart is assembled from precursor cells in the primary and the secondary (anterior) heart field in a complex process that involves numerous transcription factors. Phan and coworkers now describe how myocyte enhancer factor 2C (MEF2C) and the transcriptional repressor BOP are involved in cardiac development (see p. 2669). Mice embryos lacking MEF2C or BOP develop malformed right ventricles and outflow tracts,which implicates these transcription factors in anterior heart field development. The researchers show that Bop expression in the developing heart is downregulated in Mef2c mutant embryos and identify a MEF2C-response element in the Bop promoter that controls Bop expression in the anterior heart field. The researchers propose a network of transcription factors involved in ventricular development that,together with other recently described transcription factor networks in the heart (see Development 132, part 10), provides important insights into the aetiology of human congenital heart defects.