To date, the demonstration that the molecular components of the renin-angiotensin system (RAS) are present in adult ventricular myocytes is lacking. In addition, whether the RAS is upregulated under conditions of overload and myocyte hypertrophy in vivo remains to be determined. By employing an in vivo model of ischemic cardiomyopathy in rats, we document that adult myocytes express genes for renin, angiotensinogen, angiotensin-converting enzyme (ACE), and angiotensin II (ANG II) receptors. Moreover, renin, ACE, and ANG II receptor mRNAs increased in stressed myocytes undergoing cellular hypertrophy. At the protein level, the percentage of myocytes containing renin, ANG I, and ANG II was significantly increased in the overloaded heart. The number of binding sites for ANG II per myocyte also markedly increased under this setting. These results provide direct evidence of the existence of a myocyte RAS, which may be activated in pathological states of the heart to support myocyte growth and contractile function.