Improvement of effort angina following pure aortocoronary bypass graft surgery was related to postoperative control angiographic studies of grafts and coronary arteries in 75 unselected patients. Clinical and angiographic evaluations were carried out at approximately 1 year and at 5 to 7 years after surgery. At 1 year, 61 (81.3%) were improved (52 without angina and 9 with partial improvement by at least two functional classes), whereas 14 were unimproved (18.7%). At approximately 6 years, loss of improvement (reappearance of angina or aggravation by at least two functional classes) was observed in 22 of the 61 improved patients, representing an attrition of 36.1% over a 5-year period. Graft occlusion or a narrowing of over 50% was observed in two of the 39 patients in whom improvement had continued (5.1%), whereas it was found in six of the 22 patients (27.3%) whose results deteriorated (p < 0.05). Similarly, progression to occlusion of a preexisting stenosis of over 50% or appearance of a new stenosis of over 50% in a major coronary artery (distal to a graft or in an unbypassed artery) was observed in five of the 39 patients with continued improvement (12.8%) and in 11 of the 22 patients whose condition deteriorated (p < 0.01). Changes in a graft or in a coronary artery were noted in 63.6% (14/22) of the patients with loss of improvement as compared to only 18% (7/39) of the patients whose improvement did not deteriorate. Improvement of angina was also evaluated in all survivors among our first 500 cases who had preoperative effort angina and pure bypass surgery with or without angiographic studies. Of these 260 patients, 70.4% were angina-free or improved by two to three functional classes at 1 year, and only 41.9% at 7 years after surgery. It is concluded that the effect of aortocoronary bypass graft surgery is transient in a high proportion of patients and that deterioration of results is related to late graft modifications and progression of atherosclerosis, particularly in ungrafted coronary arteries.