The induction of transforming growth factor (TGF)-β and prepro-atrial natriuretic peptide (ANP) mRNAs represent hallmark features of pathological cardiac hypertrophy. The present study examined whether this pattern of mRNA expression was conserved in a physiological model of cardiac hypertrophy. To address this thesis, female Sprague-Dawley rats were individually housed and permitted to run freely. Voluntary exercise for 3 and 6 wk resulted in biventricular hypertrophy and increased cytochrome c oxidase activity in the triceps muscle. In the hypertrophied left ventricle, the steady-state mRNA level of the cardiac fetal gene prepro-ANP and the extracellular matrix proteins preprocollagen-α₁ and fibronectin were similar in exercise-trained and sedentary rats. By contrast, an increased expression of TGF-β₁ mRNA was observed, whereas TGF-β₃ mRNA level was unchanged in the hypertrophied left ventricle of exercise-trained compared with sedentary rats. These data highlight a heterogeneity in the regulation of TGF-β isoforms, and the increased expression of ventricular TGF-β₁ mRNA in physiological cardiac hypertrophy may contribute to myocardial remodeling.