Previous experimental and clinical studies have consistently suggested that right ventricular (RV) apical pacing has important adverse effects. Ventricular pacing, however, is required, and cannot be reduced in many patients with atrioventricular block. The SAFE-LVPACE study is a randomized controlled trial that compare the effects of conventional right ventricular (RV) pacing vs. left ventricular (LV) in patients with AV block.