BACKGROUND: Conventional pacemaker implantation induces left ventricular (LV) dyssynchrony, which might affect the LV function. We sought to evaluate the impact of different right ventricular (RV) pacing sites on the LV dyssynchrony and performance. METHODS: Comprehensive echocardiographic evaluation including the atrio-ventricular, inter- and intra-ventricular dyssynchrony based on M-mode, conventional Doppler and tissue Doppler imaging (TDI) was done before and immediately after (< 7 days) pacemaker implantation. For the LV performance, LV ejection fraction, longitudinal peak systolic velocity at the mitral annulus (S') annular or mean longitudinal velocity of the 6 basal segments (Sm) were used. These results were compared with those of 15 age matched controls. RESULTS: A total of 79 patients (48 females, mean age 63 +/- 12 years) underwent RV pacing at the apex (n = 45, group I) or the septum (n = 34, group II). After pacemaker implantation, the QRS duration was significantly increased in both groups, but the change was greater in group I (57.1 +/- 28.3 versus 32.8 +/- 40.5 msec). Both the S' and Sm were lower in pacing groups than those in controls and Sm was significantly higher in group II (4.2 +/- 1.0 versus 4.9 +/- 1.3 m/sec) than group I despite a similar LV ejection fraction. The aortic pre-ejection time and septal to posterior wall motion delay in patients with pacemaker were longer compared to normal controls, but there were no significant differences. Both the TDI velocity and strain analysis showed no difference of the dyssynchrony indices between the two groups, despite a higher tendency of Doppler strain dyssynchrony indices in the RV apical pacing group compared to those of the control. CONCLUSION: Despite the marked increase of the QRS duration after pacing, M-mode, Doppler and TDI failed to demonstrate any difference according to the pacing sites. The long-term effect of the longitudinal contraction being less affected and a smaller increase of the QRS duration in the RV septal pacing group needs to be confirmed in a longitudinal follow-up study.