Although there remains a preference for single-chamber ventricular pacing in developing countries, 70% of pacemakers presently implanted worldwide are dual-chamber systems. The number of pacing systems with cardiac resynchronization therapy capability continues to grow-a During the past 2 decades, much has been learned from clinical studies to inform optimal device mode selection and device programming for the individual patient to maximize the benefits of cardiac implantable electronic device therapy, as well as to minimize any potential adverse outcomes.