Background: It is well known that intraventricular dyssynchrony is prevalent and badly affects clinical outcome in patients with dilated cardiomyopathy. The extent of intraventricular dyssynchrony may change with exercise or pharmacological stress as left ventricular (LV) systolic function changes. However, the clinical significance of these changes is not clear. We investigated the impact of dyssynchrony changes with dobutamine infusion on the prognosis after medical therapy in these patients. Methods: Thirty six patients (20 men, age: 57 짹 13 years) with the diagnosis of idiopathic dilated cardiomyopathy were enrolled in the study. Ischemic heart disease was excluded by coronary angiography or myocardial SPECT. Comprehensive echocardiographic examination was performed at baseline and repeated 6 months after intensive medical therapy. Time from R wave on ECG to peak systolic velocity (Ts) was measured in 12 segments of LV using tissue synchronization imaging. The standard deviation of Ts (Ts-SD) was an indicator of systolic dyssynchrony. The measurements were repeated with dobutamine infusion at 10mcg/kg/min. Results: After 6 months of medical therapy, LV ejection fraction (EF) (34.6 짹 10.7 vs 40.7 짹 11.3%, p<0.05) and Ts-SD (44 짹 17 vs 34 짹 18 msec, p<0.05) improved significantly. With dobutamine infusion, LVEF and Ts-SD improved by more than 5% in 47 % and 53% of patients, respectively. Dobutamine induced improvement of Ts-SD were significantly related with dobutamine induced increase of LVEF (r=0.566, p<0.05). Improvement of Ts-SD with dobutamine was significantly correlated with improvement of LVEF at 6 month follow up (r=0.448, p<0.05). Patients who showed Ts-SD improvement with dobutamine by more than 5% had greater increase of LVEF at 6 months follow-up than those who did not (8.5 vs 0.5%, p=0.039). Conclusion: Intraventricular dyssynchrony was significantly improved with dobutamine in substantial proportion of patients with dilated cardiomyopathy and this improvement was closely associated with the favorable response to medical therapy. Dobutamine induced changes of dyssynchrony may need to be in consideration for selecting candidates for cardiac resynchronization therapy.