Between July 1980 and November 1982, there were 935 coronary angioplasties attempted at Emory University Hospital. Of these patients, 20 developed acute occlusion. Of these 20, 19 presented within 3 hr of surgery or within 3 hr after stopping a continuous heparin infusion. Five patients required emergency surgery, but in 15 nitrates, nifedipine, and/or repeat angioplasty reopened the artery and the patient could be stabilized on continuous infusions of heparin and nitroglycerin. In only one case was an occluding thrombus evident on angiographic examination. The mechanism of acute occlusion is unknown, but coronary artery spasm may play a role.