The internal mammary artery is used with increasing frequency for myocardial revascularization. However, preoperative coronary angiography does not always provide adequate visualization of subclavian arteries. If a proximal subclavian artery stenosis exists or develops in a patient who has myocardial revascularization with the internal mammary artery, graft malfunction can occur resulting in myocardial ischemia. We have identified four cases of internal mammary artery graft malfunction at our own institution and identified an additional 12 cases from the literature. These 16 cases are analyzed for age, sex, time of onset of symptoms, clinical findings, method of revascularization, and long-term follow-up. Sixty-three percent of the patients were men, and the mean age was 52.9 +/- 9.0 years. Onset of symptoms occurred after a mean interval of 25.1 months from the time of myocardial revascularization. Three patients had asymptomatic reversal of flow in the internal mammary artery as diagnosed by coronary arteriography during routine follow-up examination before 1980. One death after internal mammary artery-coronary bypass grafting was related to immediate malfunction. In the remaining 12 patients with symptomatic malfunction, all but one were treated by placement of a carotid-subclavian bypass graft with no mortality. Relief of myocardial ischemia was complete in 93% of the patients with a mean follow-up of 29.3 months. Carotid-subclavian bypass grafting appears to be the treatment of choice for the usual management of internal mammary artery graft dysfunction. Careful preoperative evaluation and postoperative follow-up of the subclavian arteries, even by simple comparison of bilateral arm blood pressure should help reduce the incidence of this syndrome.