Over the past several years, there has been growing concern over the significant deleterious effects of RV pacing, including electromechanical dyssynchrony, proarrhythmia and development of heart failure (HF). However, it remains unclear whether pacing-related ventricular dyssynchrony can translate into significant LV structural changes and produce important clinical impairment in an average pacemaker population with compromised AV conduction. Alternatively, left ventricular pacing has been shown to minimize ventricular dyssynchrony and to improve symptoms and prognosis in patients with mild to moderated systolic HF and prolonged QRS duration.