A fifty-two-year-old man received a dual-chamber pacemaker with approp
riate positioning of the leads via the right subclavian vein. About fo
ur days later he was noted to have developed a large right-sided pneum
othorax. The roentgenogram showed displacement of the heart to the lef
t and apparent displacement of the pacemaker leads with loss of the no
rmal ''J'' configuration of the atrial electrode. On resolution of the
pneumothorax, the electrode configurations returned to normal.