Purpose: Right ventricular (RV) pacing can impair left ventricular (LV) mechanics. On the other hand, biventricular pacing (BIV) can improve LV efficiency in the setting of ventricular conduction abnormalities. At present, pacing models utilize large animals, which are expensive and can not be manipulated genetically. Here, we studied whether the rodent heart can mimic pacing-related findings in human.Methods: Rats were implanted with two miniature-bipolar-hook electrodes as follows: Group A (n=6) right atrium (RA) and RV apex (RVa). Group B (n=7) RVa and posterobasal aspect of the LV (LVpb). Electrodes were attached to a connector in the back. Following recovery, two-dimensional transthoracic echocardiography was performed at baseline (no pacing) and during pacing through the electrodes at a rate slightly faster than the spontaneous heart rate. Segmental 2D circumferential strain analysis was performed (short-axis at midventricle).Results: Group A: Compared to baseline, RA pacing had no effect on LV synchrony as measured by standard deviation of segmental time to peak strain (4.22±1.66 vs. 4.05±0.79, for baseline and RA pacing, respectively, p=0.46). In contrast, RVa pacing increased the observed dyssynchrony to 11.0±1.94, (p < 0.01 vs. RA pacing). Group B: LVpb pacing and BIV pacing improved LV synchrony by 54.4±8.7% and 70.3±7.0% respectively, compared to RVa pacing (p < 0.01 for both). In both groups similar results were obtained for the standard deviation of peak segmental strain (Fig).Conclusions: In rats similarly to humans, RVa pacing induced marked LV dyssynchrony while BIV pacing created favorable LV mechanics. Thus, rodent pacing appears to mimic important features seen in humans. This model has the potential to become a reliable tool for pacing related studies. (Figure is included in full-text article.)