The VDD pacemaker is useful for sequential pacing with a single lead but carries a risk of sensing failure. This study was designed to evaluate the relationship between the relative position of atrial lead and atrial sensitivity in different postures in patients with VDD pacemakers. Atrial sensitivity determination and chest roentgenography was performed in the supine and standing position 3 months after implantation in 25 patients with VDD pacemakers. Measurements of cardiac longitudinal length (from the top of the aortic arch to the diaphragm) and distances from the floating electrode to the upper margin of the seventh thoracic vertebra (D-T7), to the top of the aortic arch (D-knob), to the lateral wall of right atrium (D-wall), and the D-knob/cardiac longitudinal length (D-Ratio) were performed. Atrial signal amplitude decreased with the standing compared to the supine position in eight patients (group I) and increased or did not change in the other 17 patients (group II). In group I, the change of the D-ratio was greater (0.073 vs 0.035, P < 0.01), and the change of the cardiac longitudinal length with standing position was greater (18.4 +/- 7.3 vs 12.1 +/- 8.8 mm, P < 0.05) than in group II. The change of atrial sensitivity was related to the change of the atrial electrode position with different postures. Decreased atrial-sensed amplitude was observed in patients who had a greater change in the cardiac longitudinal length while standing. Thus, a decrease in atrial sensitivity with standing may be predicted by the positional changes of the cardiac silhouette on roentgenography before the procedure.