The long-term effect of medical vs surgical therapy on quality of life was evaluated by New York Heart Association functional classification, severity of angina and exercise performance in 427 surviving patients with stable angina at 10 years. Surgically assigned patients had significantly more improvement in functional classification, relief of angina and exercise performance at 1 and 5 years than medically assigned patients. Relative to entry, functional classification was improved in 65% of surgically treated patients at 1 year and in 51% at 5 years, compared with 45% and 40%, respectively, of medically treated patients. Marked improvement in angina was observed in 49% of surgical patients at 1 year and in 41% at 5 years, vs 12% and 17%, respectively, in medical patients. At 10 years, quality of life was not significantly different in the 2 treatment groups: 52% of surgical patients had an improved functional classification, compared with 46% of medical patients, while 33% of surgical and 37% of medical patients had a marked improvement in angina. Exclusion of medical and surgical nonadherers had little effect on the 1- and 5-year comparisons. The 10-year treatment differences, however, were accentuated when 123 medically assigned patients who later underwent operation and who benefited from it were excluded from the analysis. In surgical patients, a strong association was observed between graft patency and functional class at 1 year, but not at 5 and 10 years. In general, patients with some or all grafts open had more improvement in functional classification than patients with all grafts closed.(ABSTRACT TRUNCATED AT 250 WORDS)