Background: Left ventricular apical rotation (LVAR) measured by speckle-tracking echocardiography (STE) has been reported to be an excellent index of LV contractility. However, the effect of right ventricular pacing (RVP) on LVAR is not known. Methods: In 6 mongrel dogs, simultaneous measurement of LV volume and pressure with a conductance catheter and LVAR was done before and after RVP. Results: LV stroke volume and LVAR decreased significantly after RVP without difference according to the pacing site. Before RVP, there was a strong positive correlation between end-systolic pressure-volume relationship(ESPVR), a gold standard of LV contractility and LVAR. However, this correlation was absent after RVP. Conclusions: LVAR is critically dependent on normal sequential activation of cardiac muscle. The long-term outcome of acute detrimental changes of LV performance by RVP needs to be determined.