To determine whether subsequent improvement in left ventricular ejection fraction can be predicted from preintervention coronary arteriograms, we divided 63 patients with acute myocardial infarction into two groups based on findings at emergency coronary arteriography at a mean of 7 hr after onset of symptoms: (1) a 'no-flow' group with an occluded infarct-related artery and no easily visible collaterals (n = 36) and (2) a 'limited-flow' group with either subtotal stenosis or total occlusion of the infarct-related vessel with intact collaterals (n = 27). Of the 63 patients, 61 underwent emergency procedures to establish reperfusion. At follow-up angiography (contrast or radionuclide) performed 12 ± 7 days after infarction, global ejection fraction had increased significantly in patients with limited flow to the infarct zone and 'successful' early reperfusion intervention due primarily to a significant increase in the regional ejection fraction in the infarct zone. Global ejection fraction fell significantly between baseline and follow-up in patients with no flow to the infarct zone and 'unsuccessful' early reperfusion intervention due primarily to a fall in the regional ejection fraction of the noninfarct zone. Global and regional ejection fractions did not change significantly in patients with no flow to the infarct zone and successful early reperfusion or in patients with limited flow to the infarct zone and unsuccessful early reperfusion intervention. The elapsed time before reperfusion did not relate significantly to the change in either regional or global ejection fraction. However, the magnitude of improvement in both global and regional ejection fraction at follow-up was greater among patients with anterior infarcts than among those with inferior infarcts, possibly because baseline ejection fraction was lower in patients with anterior infarcts. These data indicate that among patients with acute myocardial infarction undergoing emergency coronary arteriography at a mean of 7 hr after onset of symptoms, improvement in global ejection fraction is unlikely to occur even after a successful early reperfusion intervention in the absence of preserved flow to the infarct area. However, among patients with subtotally occluded infarct-related arteries or significant collateral blood flow to the infarct zone, subsequent improvement in global and regional ejection fraction in the zone of myocardial infarction frequently occurs. Improvement in both global and regional ejection fraction may be more readily demonstrated in patients initially having more severe depression of these parameters.