AbstractProperly timed atrial systole may alter systolic performance by the mechanism of Starling's law of the heart, which states that the extent of systolic myocardial fiber shortening is dependent on the degree of diastolic fiber stretch, or preload. However, the atrial contribution to physiological need and thus is critical in developing the proper cardiac output response to exercise. Current generations of permanent pacemakers, which may have a combination of dualchamber and sensor technologies, will permit the restoration of normal cardiac physiology (AV synchrony and/or rate response) in most patients.