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Previous experimental and clinical studies have consistently suggested that right ventricular (RV) apical pacing has important adverse effects. Ventricular pacing (VP), however, is required, and cannot be reduced in many patients with atrioventricular (AV) block. The PREVENT-HF study was an international randomized trial that explored differences in left ventricular (LV) remodelling during RV apical vs. biventricular (BIV) pacing in patients with AV block.Patients with an expected VP prevalence ≥80% were assigned to RV apical or BIV pacing. The primary endpoint was the change in LV end-diastolic volume (EDV) >12 months. Secondary endpoints were LV end-systolic volume (ESV), LV ejection fraction (EF), mitral regurgitation (MR), and a combination of heart failure (HF) events and cardiovascular hospitalizations. Overall, 108 patients were randomized (RV: 58; BIV: 50). Intention to treat and on-treatment analyses revealed no significant differences in any of the outcomes. Analysis of covariance (ANCOVA) difference for treatment according to randomization (in mL): LVEDV −3.92 (−18.71 to 10.85), P= 0.6; LVESV −1.38 (−12.07 to 9.31), P= 0.80; LVEF 2.47 (−3.00 to 7.94), P= 0.37. Analysis of covariance difference for the on-treatment analysis: LVEDV −4.90 (−20.02 to 10.22, PP= 0.52; LVESV −6.45 (−17.28 to 4.38), P= 0.24, LVEF 2.18 (−3.37 to 7.73), P= 0.44. Furthermore, secondary endpoints did not differ significantly.This study did not demonstrate significant LV volume differences >12 months between RV apical and BIV pacing for AV block. Thus, BIV pacing cannot be recommended as a routine treatment for AV block in these patients. However, the results encourage and inform the design of subsequent larger trials with higher power for detecting small volume changes. ClinicalTrials.gov Identifier: NCT00170326.