Objective: To evaluate the effects of treatment on left ventricular (LV) performance and endothelial function in patients with acromegaly. Method: Nineteen patients with active acromegaly (AA), 18 patients with cured/well-controlled acromegaly (CA), and 25 healthy control subjects were studied. LV performance was evaluated by two-dimensional/Doppler echocardiography and Doppler tissue imaging (TDI). Flow-mediated dilatation (FMD) was measured by B-mode ultrasound. Endothelial cell markers; thrombomodulin (TM), and P-selectin were also measured. Results: Tei index was higher than the control subjects in both acromegaly groups. The ratio of early and late diastolic annular velocities (Em'/Am') was significantly lower in the AA group than the other groups (P < 0.05). FMD in both acromegaly groups was significantly lower than the controls (P < 0.001) but difference between acromegaly groups was not significant (P > 0.05). In the CA group, P-selectin was higher than the controls and was even higher in the AA (P < 0.05). TM was significantly higher in the active group (P < 0.05) and not different than the controls in the CA group. Conclusion: TDI determine LV performance changes in acromegaly earlier than conventional echocardiographic methods. Endothelial function both in the form of FMD and endothelial cell markers is impaired in acromegaly. While in cured acromegaly endothelial cell injury, as evidenced by TM levels, is decreased, endothelial dysfunction still persists. (Echocardiography 2010;27:990-996).