Twenty-six consecutive patients had measurement of ejection fraction by gated blood-pool imaging at rest and during isometric exercise, following recovery from an uncomplicated myocardial infarction. We found there was a highly significant fall in ejection fraction at rest from 56 +/- 3% to 43 +/- 3% during isometric exercise (p less than 0.0001). There was a dramatic fall in ejection fraction during isometric exercise in some patients with a normal resting value. These patients may be a cause for concern. Our preliminary findings suggest these latter patients are at risk for future cardiac events such as, unstable angina, further myocardial infarction and future coronary bypass surgery.