Background: The pump function during exercise can be disturbed not only in hypertensives with coronary artery disease (CAD), but also in those with a normal angiogram. Methods: In 10 hypertensive patients (group 1; aged 52±4 years, 1 men, 9 women) with ST segment depression during exercise and concomitant angina pectoris but normal coronary angiograms (microangiopathy) and without left ventricular hypertrophy (LVMI <110 g/m<sup>2</sup>), the left ventricular function at rest and during exercise was studied by cardiac catheterization and compared with 10 hypertensives with CAD (group 2; aged 57.6±4 years, 7 men, 3 women) and 10 hypertensives without ST segment depression (group 3; aged 51.8±5 years, 10 men) before and after intravenous administration of 1.25 mg enalaprilat. Results: The pulmonary capillary wedge pressure (PCWP) was normal at rest and pathologically increased at 60±13 W only in groups 1 and 2 (27.2±3 and 32.2±8 mm Hg, respectively), but not in group 3 (12.2±4 mm Hg; p<0.001). At the identical load level, the PCWP in patients with microangiopathy (group 1) was significantly (p<0.01) reduced after enalaprilat (–21.7%) and even normalized in 5 of 10 patients. This was accompanied by a significant (p>0.01) decrease in ST segment depression (–73.9%) and in the occurrence of angina pectoris, despite the fact that the rate–pressure product as a measure of myocardial oxygen consumption was significantly (p<0.05) increased. Also in patients with CAD enalaprilat had a significant effect on PCWP (p<0.01), ST segment depression (p<0.01), occurrence of angina pectoris (p<0.001), cardiac index (p<0.05), and stroke index (p<0.05) during exercise. In group 3 there were no significant changes in PCWP, cardiac index, and stroke index after enalaprilat either at rest or during exercise. Conclusion: The functional improvement under the action of enalaprilat suggests that the advantages of the drug may be mediated mainly through an increase in myocardial blood flow and that angiotensin II might be involved in the restricted increase in coronary blood flow during dynamic exercise in hypertensives with coronary microangiopathy.