The present study was undertaken to examine the effects of volume overload on cardiac gene expression and the possible role of angiotensin AT₁ receptor in such expression. Cardiac volume overload was prepared by abdominal aortocaval shunt in rats. Rats with aortocaval shunt were treated with 1) vehicle, 2) an angiotensin AT₁ receptor antagonist, CS-866 (10mg/kg/d), or 3) an angiotensin-converting enzyme inhibitor, temocapril (10mg/kg/d), for 7 days. Cardiac tissue mRNA was measured by Northern blot analysis with specific probes. Aortocaval shunt not only caused cardiac hypertrophy but also upregulated the gene expression of atrial natriuretic polypeptide, collagen III, and downregulated Ca²⁺- ATPase expression in the left ventricle. These changes were prevented by treatment with CS-866, while temocapril failed to normalize left ventricular Ca²⁺-ATPase expression. Unlike the left ventricle, the significant downregulation of α-myosin heavy chain and transforming growth factor-β3 by aortocaval shunt was observed in the right ventricle, and CS-866 normalized this decreased expression of transforming growth factor-β3. The left and right atria showed increased expression of collagen type I as well as of collagen type III and atrial natriuretic polypeptide, and these increases were more effectively prevented by CS-866 than by temocapril. Thus, the effects of cardiac volume overload on cardiac performance-related gene expression differ between the ventricles and atria. Our results suggest that AT₁ receptor partially contributed to volume overload-induced changes in cardiac gene expression and that AT₁ receptor antagonists and angiotensin-converting enzyme inhibitors have different effects in this model of cardiac hypertrophy. (Hypertens Res 1997; 20: 133-142)