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Background: Recent data suggest that contractile reserve in dysfunctional but viable myocardium during low-dose dobutamine infusion might be elicited not only by a direct inotropic stimulation but also by an increase in coronary blood flow. Aim of the study was to evaluate the effects of low-dose dobutamine on myocardial perfusion and function in asynergic but viable myocardium., Methods: Nineteen patients with coronary artery disease and severe regional dysfunction were studied. Both regional ventricular function and myocardial perfusion were assessed at rest (PRE), during low-dose dobutamine (DOB) and, in twelve patients, after revascularization (POST). Regional ventricular function was evaluated with two-dimensional echocardiography using a score index ranging from 1 to 4. Myocardial perfusion was studied using Tc-99m-sestamibi Single Photon Emission Tomography (SPET); uptake defects were graded from 0 (normal) to 4 (absent uptake). For both evaluations the left ventricle was divided in 16 segments and two vascular territories were considered., Results: Low-dose dobutamine elicited contractile reserve in 12 of 24 asynergic vascular territories (DOB+). Compared with PRE scintigraphy, DOB SPET showed perfusion improvement in 10/12 DOB+ and in 3/12 DOB- asynergic territories (p = 0.006). Mean uptake score decrease significantly in DOB+ (from PRE SPET 21.0 +/- 7.2 to DOB SPET 17.6 +/- 7.1; p = 0.0005) but not in DOB- (from SPET PRE 19.0 +/- 5.3 to SPET DOB 19.5 +/- 6.8, p = NS) abnormal territories. Fourteen asynergic territories underwent revascularization. Among them, 9 showed functional recovery after intervention (viable myocardium) and 5 showed no changes (fibrotic myocardium). A functional improvement under dobutamine was observed in 7 viable and in 1 fibrotic territories. Conversely, perfusion improved under dobutamine in 8 viable and in one fibrotic territory. After revascularization the perfusion defect score decreased significantly in viable territories (from PRE SPET 22.1 +/- 7.9 to POST SPET 13.3 +/- 6.6; p = 0.00001) but not in fibrotic regions (from PRE SPET 17.8 +/- 6.0 to POST SPET 15.6 +/- 4.9)., Conclusions: In asynergic myocardium contractile reserve elicited by low-dose dobutamine is associated in most cases with an improvement in Tc-99m-sestamibi uptake. This suggests a possible link between increased blood flow and functional improvement during dobutamine in viable myocardium.