Hemodynamic and structural changes of the heart and large arterial vessels were studied in normotensive and spontaneously hypertensive rats following 12-week administration of converting enzyme inhibitor (perindopril, 2 mg/kg daily by gavage). In both strains, a significant blood pressure reduction was observed. In normotensive rats, the hemodynamic changes involved significant increase in systemic arterial compliance, whereas slight changes in left ventricular weight and aortic medial thickness were observed. In hypertensive rats, the increase in compliance was relatively small, whereas there was a major reduction in medial thickness. The reduction of the media thickness was much more pronounced than that of the left ventricular hypertrophy. In both strains, the collagen density in the subendocardial layers of the left ventricle was significantly decreased in treated vs untreated groups. The isomyosine profile of the left ventricular muscle was also modified by ACE inhibition with an increase in the V1 form and a decrease in the V3 form. The present results suggest that the cardiac and arterial changes observed following long-term converting enzyme inhibition do not strictly parallel the blood pressure changes in hypertensive rats. Dissociation between cardiac and arterial changes may be observed.