Abstract Background pacemaker induced cardiomyopathy or transient impairment of the left ventricle (LV) function could be common collateral effects of the prolonged right ventricle (RV) pacing in patients with a pacemaker (PM) and pre-existing intra-ventricular conduction disturbances. However, the impact of RV pacing-site on RV performance of patients with right bundle branch block(RBBB) is still under-investigated. Purpose to study the effects of RV pacing in the mid-septal versus apical site on the morpho-functional performance of RV in patients undergoing permanent PM implantation. Methods We prospectively enrolled consecutive patients with a pre-existent complete RBBB and undergoing dual-chamber PM implantation in our institution. We randomized the patients 1:1 to receive the RV catheter fixed either in the apex or in the mid-septal position. Patients with LV systolic dysfunction (LVEF <50%), severe valvulopathies, left bundle branch block (LBBB), or preserved intraventricular conduction were excluded. Patients who received PM implantation were evaluated both at baseline and after two months with a 12-lead ECG, 2D, and 3D echocardiogram with analysis focused on RV performance according to the guidelines of the European Association of Cardiovascular Imaging. Results a total of 22 patients were randomized in the study, 11 (50%) received RV catheter positioned in the apex and 11 (50%) in the mid-septum, respectively. No baseline differences were recorded between the two groups in clinical characteristics, ECG and echocardiographic parameters. At 2 months follow up, there were no statistically significant difference in the % of RV pacing between the two groups. Nonetheless, RV mid-septal group showed significantly shorter duration of the stimulated QRS (146 ± 12 msec vs. 161 ± 20 msec, p = 0.05), significantly reductions in the RV dimensions (pre: 42 ± 8 mm vs. post: 37 ± 7 mm, p = 0.05) telediastolic area (pre: 12 ± 3 cm2/m2 vs post: 9 ± 4 cm2/ m2, p = 0.02) telediastolic volume (pre: 55 ± 16 ml/m2 vs post: 50 ± 17 ml/m2, p = 0.02) and a significant improvement of RV ejection fraction (pre: 54 ± 9% vs post: 57 ± 11%, p = 0.02) than patients in the RV-apical group. Moreover, patients in the RV-apical group showed significant lowering in the GLS of the LV (pre: -16 ± 3% vs post: -11.7 ± 3%, p <0.001) and in the TAPSE (pre: 23 ± 5 mm vs post: 21 ± 2, p = 0.07) at follow up. Conclusions In this study, mid-septal pacing seems associated with a better morpho-functional RV performance than apical pacing in patients with pre-existent RBBB undergoing permanent PM implantation.