Background:Patients with permanent pacemakers (PM) are at high risk of developing atrial fibrillation (AF). Left atrial (LA) function, however, in patients with PM has not been investigated. Method: 37 patients with single and dual chamber PM at least 12 months, previously diagnosed with sick sinus syndrome with intact atrioventricular conduction, were enrolled. Atrial lead was positioned in the right atrial appendage and ventricular lead in the right ventricular apex (RVA). The LA diameter, LA volume index, and mitral inflow parameters were measured. Longitudinal peak strain and strain rate (SR) were obtained from the basal left atrial free wall and the inter-atrial septum in the apical 4 chamber view using the tissue Doppler strain. Standard deviation of the time to peak systolic velocity in ejection period (SD-Ts) among the 12 left ventricular (LV) segments were analyzed by tissue synchronization imaging (TSI). All the parameters were compared with 20 healthy controls. Results: There were significant differences in the LA size and LV filling pressure represented by E/E���between patients with RVA pacing and controls. The values of the peak systolic LA strain and SR, peak early diastolic SR and late diastolic SR were also significantly lower in patients with RVA pacing (table). In addition, there was significant difference in the intraventricular delays of SD-Ts (dyssynchrony index) between groups. Conclusions: Chronic RVA pacing can impair LA function and induce LV mechanical dyssynchrony. The lower values of atrial strain and SR suggested that active contraction and passive stretching of LA wall may be impaired in patients with RVA pacing, which would be predisposing factor in development of atrial fibrillation.