Abstract To compare Endothelin (ET) production and genes expression of ET-1 and ET A receptor (ET AR) between broiler and layer chickens during rearing, semi-quantitative RT-PCR and enzyme immunometric assay were performed in the heart ventricles and serum. There were gradual elevations of ET-1 and ET AR mRNAs in the left ventricle of broiler and layer chicken groups that were mainly significant ( P < 0.05) at 28, 35 and 42 days of age with compared to previous days whereas were not significant between two groups. These gradual elevations of ET-1 and ET AR mRNAs were also observed in the right ventricle that were significant ( P < 0.05) at 28, 35 and 42 days of age in broilers and 42 days of age in layers with compared to previous days. Increasing of these mRNAs in the right ventricle of broiler chickens were significantly ( P < 0.05) more than layer chickens at 28, 35 and 42 days. Serum ET in broilers was significantly ( P < 0.05) higher than layer chickens at 28 and 42 days of age. It is concluded that circulating ET and cardiac ET-1, ET AR genes expression is higher in broiler chickens than in layer chickens particularly after 21 days of age. It is probably that these breed differences make broiler chickens to be more susceptible to Endothelin related-cardiomyopathies such as congestive heart failure and ascites.