Background and Objectives竊� An association between stress and cardiovascular diseases has been described. However, the underlying biological mechanisms have not been fully elucidated. We investigated the left ventricular (LV) and endothelial function in patients with fibromyalgia (FM) and its relationship with the degree of chronic emotional and physical stress. Methods: Global and segmental longitudinal deformation parameters of LV were examined in 55 consecutive postmenopausal women (mean 53짹5 year-old) with FM, and 35 healthy controls by means of standard and 2-dimensional strain echocardiography. Endothelial function was measured by brachial artery flow-mediated dilatation (FMD, endothelium dependent) and response to 40 µg of sublingual nitroglycerine (NTG-induced dilatation, endothelium independent) by use of high-resolution ultrasound. Patients with hypertension, coronary artery disease or diabetes were excluded. FM patients completed the fibromyalgia impact questionnaire (FIQ) which were composed with physical and feel score, brief fatigue inventory (BFI), and Beck depression inventory (BDI). The FM patients were divided into 2 groups based on the sum of the FIQ (group A: FIQ 50, group B: <50) Results: LV systolic function, LV chamber dimension, and LV wall thickness were normal in FM group. There were no significant differences in the mitral inflow parameters and myocardial performance index between the FM and control group, among group A, B and control. The peak systolic LV strains of fibromyalgia group were significantly lower than those of control group in all directions of view. The Global LV strain was also significantly lower than that of controls (-19.5짹3.3% vs. -22.8짹9.6%, p=0.003), and was significantly reduced in group A than B (-18.6짹3.1% vs. -22.7짹1.5%, p=0.001). There were significant differences in the value of FMD (5.73.9% vs. 7.01.4%, p=0.008) between the FM patients and control, and same result in the NTG-induced dilatation (12.55.1% vs. 14.72.5%, p=0.006). The values of NTG-induced dilatation were significantly different from each other among group A, B, and control (p=0.006) in contrast to the FMD (p=0.287) Conclusion: Chronic emotional and physical stress of the FM patients may exert negative effects on the left ventricular and endothelial function. There were significant differences in the left ventricular and endothelial function of the FM patients according to the severity of stress. This study provides a possible mechanism by which FM syndrome is associated with increased risk of cardiovascular dysfunction.