Hey2 knockout hearts in addition show evidence of cardiomyopathy in the ventricles, which corresponds well to the fact that ventricular cardiomyocytes express only Hey2, but not Hey1 or HeyL. We therefore tested dissected ventricles of Hey2−/− embryos at E14.5 for deregulation of Hey target genes. The gene discussed is HEY1; the disease is cardiomyopathy.