Dysfunctional left ventricular (LV) segments showing contractile reserve during dobutamine stress echocardiography (DSE) are considered viable myocardium; functional recovery is expected after revascularization. Many segments, however, particularly mildly hypokinetic segments, do not recover. The reason for this failure is unknown. Two-dimensional echocardiography at rest and low-high-dose DSE were performed before revascularization in 114 consecutive patients with ischemic cardiomyopathy. Two-dimensional echocardiography at rest was repeated after 9 to 12 months. Segmental function was scored by a 5-point grading score. Functional recovery after revascularization was assessed in mildly hypokinetic (score 2, group I) and severely dysfunctional segments (score 3 to 5, group II). For each segment, functional recovery was defined as an improvement in functional score of > or =1 grade compared with the baseline score at rest. During low-dose DSE (up to 10 microg/kg/min), 183 group I segments (68%) and 438 group II (39%) segments had contractile reserve (p <0.0001). However, functional recovery was observed less frequently in group I segments (41%) than in group II segments (55%) with contractile reserve (p <0.005). During high-dose DSE (up to 40 microg/kg/min), in the group I segments with contractile reserve at the low dose, the sustained improvement pattern (indicating subendocardial scar) was prevalent (73%). After revascularization, 73% of segments with sustained improvement did not recover. Conversely, the biphasic response (indicating ischemically jeopardized myocardium) was observed only in 27% of group I segments. Functional recovery occurred in 39 of these segments (78%) (p <0.001 vs sustained improvement). Hence, mildly hypokinetic segments probably indicate the presence of subendocardial scars, and may explain the failure in functional recovery after revascularization.