The increased cost and potential confusion of dual chamber pacing systems are only justified by the improved quality of life and hemodynamic benefits available to recipients of these units. This presupposes, however, that the system is functioning properly, that P waves are properly sensed, and that atrial stimuli, when released, are effective. Confirmation of ventricular capture and sensing is not without its occasional difficulties, yet it is an order of magnitude easier than is confirmation of atrial capture, particularly in dual unipolar pacing systems. The large stimulus artifact followed by an RC decay curve associated with the afterpotential as recorded with the usual electrocardiograph machine may obscure the relatively diminutive electrocardiographic representation of atrial depolarization. When not visualized in any of the standard bipolar and unipolar lead systems, then Lewis leads and esophageal leads, echocardiography, phonocardiography, and other recording techniques may all aid in the confirmation of atrial capture. However, these require additional equipment, expense, and time. They may not be immediately available when the patient is seen in follow-up and the need to do something extra may induce in the patient additional psychological fear that the system is not functioning properly. Although one commonly performs the follow-up evaluation while monitoring only a single electrocardiographic lead, if atrial capture is not visualized in that lead, a careful assessment of all 12 standard leads will usually identify one in which capture can be confirmed. However, in approximately 10% of cases, a P wave will not be seen, mandating other studies. This paper reviews many of the programming techniques that permit confirmation of atrial capture without having to resort to other diagnostic tests or complex and potentially invasive procedures. For the remainder of this paper, it will be assumed that P waves were not visualized in any of the standard electrocardiographic leads. The illustrations designed to demonstrate other features that permit deduction of atrial capture, however, may also show visible P waves, since not all of the figures were obtained from patients with this specific problem. Table I lists the programmable parameters that are needed in this endeavor, either in combination or alone. [ABSTRACT FROM AUTHOR]