The effect of supine leg exercise and an infusion of isoprenaline (2 µg/min) have been compared in 9 patients with angina pectoris and 8 normal control subjects. Left ventricular ejection fraction was measured by radionuclide angiography using the gated blood pool technique. The normal subjects increased their ejection fraction from 0.57 ± 0.02 at rest to 0.71 ± 0.02 during exercise, and 0.76 ± 0.03 during isoprenaline infusion. In patients with angina pectoris, the resting ejection fraction of 0.47 ± 0.04 decreased to 0.35 ± 0.04 during exercise but increased to 0.63 ± 0.06 during isoprenaline infusion. Our results suggest that the changes in ejection fraction probably depend on the changes in left ventricular segmental wall motion. When dyskinesia is increased, as with exercise, the ejection fraction declines, but when dyskinesia is unaffected or improved, as with isoprenaline, the ejection fraction increases.