The dobutamine echocardiographic test (DET) is frequently used in coronary artery disease to detect viable myocardium, but few data are available about its role in idiopathic dilated cardiomyopathy (IDCM). The aims of this study were to evaluate the clinical role of DET and the prognostic implications of the 'contractile reserve' in patients with IDCM treated with optimal medical therapy, including beta-blockade (BB). A total of 51 patients with IDCM underwent DET at diagnosis. A positive response to DET (DET+) was judged to be a significant increase (> or =10 points) in left ventricular ejection fraction (LVEF) with a peak value > or =40%, and a reversed restrictive left ventricular filling pattern (RFP) if present at baseline study. Improvement at follow-up was defined according to combined clinical and echo-Doppler criteria. In all, 22 patients (43%) were classified as DET+. DET+ patients were less symptomatic (P<0.001), with lower heart rate (P<0.01), less enlarged left and right ventricles (P<0.0001 and P<0.05), higher LVEF (P=0.0001), less frequent RFP (P=0.01), and lower pulmonary pressure (P<0.01). At follow-up (34+/-16 months), 21 patients had improved, while four had died and seven had received a transplant. Among clinical data, NYHA classes I-II (OR=0.25, P=0.07) and BB dosage (OR=0.97, P<0.005) were significantly associated with higher transplant-free survival at multivariate analysis. The addition of DET+ (OR=0.34, P<0.05) showed a moderate but significant improvement of sensitivity, but the predictive power of the model remained low (sensitivity, 0.67; specificity, 0.55). Absence of left bundle branch block (OR=0.27, P<0.01) and BB dosage (OR=1.03, P<0.005), but not DET+, were predictive of improvement. In patients with IDCM, DET response is associated with a more favourable outcome, since it suggests an earlier stage of the disease. However, in the light of our data, the incremental prognostic power of DET response compared to clinical evaluation at enrollment, despite being significant, seems to be of limited clinical value. Further studies should be carried out in order to clarify the prognostic value of DET in IDCM patients.