"Stunned" myocardium prevents the assessment of myocardial salvage after streptokinase. In order to unmask "stunning," we sought to evaluate left ventricular inotropic contractile reserve of paatients after streptokinase. Radiionuclide ventriculograms were obtained in 75 consecutive patients 2 weeks after myocardial infarction, at rest and during intravenous isoproterenol infusion. Resting and isoproterenol-stressed ejection fractions were compared in the patent and closed-infarct vessel groups. Although there was no difference in the resting ejection fractions between the patent group (0.48 ± 0.02) and the closed group (0.48 ± 0.02), isoproterenol increased the ejection fractions in the patent group (↑ 0.14 ± 0.01) significantly more than in the closed group (↑ 0.06 ± 0.01) (p < 0.0001). Thus, despite identical resting ventricular function, the greater inotropic contractile reserve in the patent infarct vessel group suggests that restoration of blood flow in acute myocardial infarction salvages myocardium. © 1986.