Objectives. We evaluated the use of fluorine-18 fluorodeoxyglucose (FDG) and single-photon emission computed tomography (SPECT) to predict improvement of left ventricular ejection fraction (LVEF) after revascularization. Background. FDG SPECT has recently been proposed for assessment of myocardial viability. However, FDG SPECT still awaits validation in terms of predicting improvement of contractile function after revascularization in patients with poor left ventricular (LV) function. Methods. Fifty-five patients with contractile dysfunction (including 22 with LVEF <30%) underwent FDG SPECT during hyperinsulinemic glucose clamping and early thallium-201 SPECT (to assess perfusion). Improvement of LV function was evaluated 3 months after revascularization with echocardiography and radionuclide ventriculography. Results. The 55 patients were arbitrarily classified into two groups: 19 with three or more viable, dysfunctional segments on FDG SPECT and 36 with less than three viable, dysfunctional segments. LVEF increased significantly in the first group, from 28 ± 8% (mean ± SD) before to 35 ± 9% (p < 0.01) after revascularization. In the second group, LVEF remained unchanged after revascularization (45 ± 14% vs. 44 ± 14%, p = NS). The 22 patients with severely depressed LV function were similarly classified into two groups: 14 with three or more viable segments on FDG SPECT in whom LVEF improved significantly (25 ± 6% vs. 32 ± 6%) and 8 with less than three viable segments in whom LVEF remained unchanged (24 ± 6% vs. 25 ± 6%). Conclusions. This study shows that FDG SPECT can identify patients in whom LV function improves after revascularization. Because SPECT is widely available, this technique may contribute to more routine use of FDG for determination of viability.