The effectiveness of intra-aortic balloon pumping in augmenting ventricular performance during acute myocardial ischemic syndromes was determined by noninvasive multigated cardiac blood pool imaging. Nine patients with unstable angina refractory to medical therapy and nine patients with acute myocardial infarction complicated by congestive heart failure were studied on and off intra-aortic balloon pumping (IABP). End-diastolic and end-systolic volumes were significantly reduced by IABP in both unstable angina and myocardial infarction. Analysis of ventricular wall motion demonstrated improved segmental contraction during IABP in all seven unstable angina patients with regional wall motion abnormalities. No significant improvement in regional contraction was observed in the nine patients with acute myocardial infarction. During IABP, percent ventricular asynergy decreased significantly (28.2%; P < 0.01) among patients with unstable angina but demonstrated no significant fall (4.4%; P = NS) for patients with myocardial infarction. Thus, IABP enhances contraction of ischemic but not infarcted myocardium and effectively improves ventricular function by reducing end-diastolic and end-systolic volumes.