The development of atrioventricular pacing was principally aimed at improving cardiac hemodynamics and creating a more physiological heart rate control. Hemodynamic studies have clearly shown the benefit of this approach in many patients, particularly those with decreased left ventricular compliance in whom atrial activity contributes significantly to cardiac output. Lack of synchronization between the upper and lower chambers of the heart caused by pacing the ventricle alone can result in a constellation of symptoms commonly referred to as "pacemaker syndrome".