The respective roles of peripheral and myocardial determinants of exercise ventricular performance were studied in 10 normal volunteers and in 9 mildly hypertensive patients without evidence of coronary disease. Hemodynamic measurements and equilibrium blood pool scintigraphy were simultaneously performed at rest and during maximal upright exercise. In hypertensive patients, mean systolic and diastolic blood pressure were, respectively, 199 +/- 23 and 102 +/- 12 mm Hg at rest, and 271 +/- 28 and 113 +/- 8 mm Hg at peak exercise. Ejection fraction response to exercise was normal (increase by more than 5%) in 4 hypertensive patients (normal hypertensive group: 63 +/- 4 to 77 +/- 6%) and in volunteers (65 +/- 3 to 78 +/- 4%) and abnormal in 5 hypertensive patients (abnormal hypertensive group: 66 +/- 6 to 58 +/- 10% at peak exercise). The abnormal response in the abnormal hypertensive group was not due to an inadequate decrease in systemic vascular resistance during exercise. By contrast, the ratio systolic blood pressure/end-systolic volume, an index of contractility, decreased by 2.3 +/- 4.9 in the abnormal hypertensive group, whereas it increased by 9.8 +/- 9.1 in the normal hypertensive group and by 7.3 +/- 2 in volunteers. Thus, abnormal exercise ejection fraction response in mild hypertension was not related to increased afterload but rather to intrinsic myocardial factors.