To investigate the effects of transforming growth factor-beta1 (TGF-beta1) and signal protein Smad3 on rat myocardial hypertrophy.The total protein was analysed by flow cytometer assay to judge the hypertrophy of myocardial cell incubated with different level of TGF-beta1 in cultured myocardial cells of neonatal rats. The models of rat cardiac hypertrophy were produced with constriction of the abdominal aorta. At the different time after the operation, the rats were killed, and the left ventricular mass indexes (LVMl) were investigated. The mRNA expressions of TGF-beta1 and Smad3 of cultured cells and hypertrophic left ventricles were assessed by RT-PCR, the protein expressions of Smad3 were assessed by Western blot.In cultured neonatal myocardial cells, different level TGF-beta1 could significantly increase the total protein, and TGF-beta1 (3 ng/ml) could increase the expression of mRNA and protein of Smad3 and continued for 8 h of cultured cardiomyocytes. The LVMI and the expression of TGF-beta1 mRNA and Smad3 mRNA/protein of hypertrophic left ventricle were increased at the 3rd day after the operation and continued for 4 weeks. The peak expression of them was in 2 weeks after operation.TGF-beta1 has the effects on rat myocardial hypertrophy, signal protein Smad3 is included in the pathologic progress of rat myocardial hypertrophy.