Echocardiography showed increased left ventricular (LV) size, mass, and dyssynchrony induced by 6 mo of right ventricular septal‐dependent pacing. A, The left ventricular end‐diastolic diameter (LVEDD) of the pacing group at 6‐mo follow‐up was significantly larger than that at the baseline (P=0.028). B, LV mass index increased in the pacing group at 6‐mo follow‐up compared with baseline. C, No difference in LV ejection fraction (LVEF) was measured after the 6‐mo observation period in the pacing and sham control groups. D, The pacing group had significantly increased septal‐to‐posterior wall motion delay (SPWMD) compared with the sham control group in the immediate postoperative period (P=0.004). Likewise, the pacing group exhibited significantly increased SPWMD compared with the sham control group at the 6‐mo follow‐up before euthanasia (P=0.004). However, no significant change in SPWMD was identified after the 6‐mo observation period in the pacing group. E, The pacing group had significantly increased septal‐to‐free‐wall radial strain compared with the sham control group in the immediate postoperative period (P=0.010). Likewise, the pacing group exhibited significantly increased septal‐to‐free‐wall radial strain compared with the sham control group at the 6‐mo follow‐up before euthanasia (P=0.005). However, no significant change in septal‐to‐free‐wall radial strain was identified after the 6‐mo observation period in the pacing group. Gray bar: sham control group; black bar: pacing group.