The aim of this study was to assess the prognostic value of the amount of dysfunctional but viable myocardium in revascularized patients with coronary artery disease and left ventricular dysfunction. To quantify the amount of dysfunctional but viable myocardium, low-dose dobutamine echocardiography was performed. The wall motion was scored using a 16-segment model. The dysfunctional segments were defined as viable if they exhibited functional improvement of at least 1 grade with any dose of dobutamine, or only worsening with dobutamine infusion. Two hundred and twenty patients were revascularized and followed-up for a mean period of 33+/-23 months (range, 0-86) for cardiac-related death and hospitalization for heart failure. Standard follow-up echocardiography was performed 3-6 months after revascularization. Receiver operating characteristic curve analysis identified six dysfunctional but viable segments as the optimal cutoff value for discriminating patients with and without risk of cardiac events. Thirty-eight patients exhibited a large amount of dysfunctional but viable myocardium (>or=6 segments, group A), 103 patients had a small amount of dysfunctional but viable myocardium (2-5 segments, group B), and 79 patients were found to have dysfunctional myocardium irreversibly damaged (group C). Similar baseline left ventricular ejection fractions of 36+/-4, 34+/-5, 35+/-5% in groups A, B, and C increased to 46+/-6% (P<0.01 versus baseline and versus groups B and C), to 39+/-5% (P<0.01 versus baseline and group C), and to 36+/-7% (P<0.01 versus baseline), respectively, after revascularization. The greatest functional improvement after revascularization in group A patients was accompanied by a lower frequency of cardiac events during follow-up (1 vs. 27 in group B, P<0.01, and versus 18 in group C, P<0.01) and by a better cardiac event-free survival according to Kaplan-Meier survival analysis (P<0.01 versus groups B and C, respectively). In conclusion, in revascularized patients with coronary artery disease and moderate-to-severe left ventricular dysfunction, the presence of >or=6 dysfunctional but viable segments identifies patients with the best prognosis.