Coronary bypass surgery: is the operation different today? Patients undergoing coronary bypass grafting have undergone an evolution in recent years. To document this change, we analyzed two groups of patients in 1981 (n = 1586) and 1987 (n = 1513) to document preoperative and postoperative variables important in determining immediate morbidity and mortality after isolated coronary bypass. Between 1981 and 1987, patients were found to be older (greater than or equal to 70 years, 8.7% versus 21.8%, p less than 0.0001), more often diabetic (15% versus 24%, p less than 0.0001), have a greater prevalence of triple vessel disease (14.5% versus 46.1%, p less than 0.0001), and have more left ventricular dysfunction (ejection fraction 0.60 +/- 14 versus 0.54 +/- 13, p less than 0.0001). To facilitate analysis and because of overlap between subgroups, we subdivided patients into three subgroups for statistical comparison of the years 1981 and 1987: subgroup I, no prior procedure (n = 1546 in 1981 and 1396 in 1987); subgroup II, optimal group (n = 503 in 1981 and 292 in 1987, and defined as no prior procedure, ejection fraction greater than or equal to 0.50 and age less than 65 years); subgroup III, patients having reoperations (n = 40 in 1981 and 117 in 1987). Internal mammary artery grafting was infrequently used in 1981 but was used in 72.1% in 1987. Major postoperative morbidity between the 2 years for the total population increased significantly: need for intraaortic balloon pumping, 1.4% versus 4.7%, p less than 0.0001; myocardial infarction 3.5% versus 5.5%, p less than 0.008; stroke, 1.4% versus 2.8%, p less than 0.008; and wound infection, 1.0% versus 3.0%, p less than 0.001. Wound infection (all types) in 1987 was increased sevenfold in patients having a perioperative myocardial infarction (0.7% versus 5%, p less than 0.0001). For young patients with good left ventricular function (subgroup II), there was no increase in these morbid events between 1981 and 1987. Hospital mortality in the total population increased significantly between 1981 and 1987 from 1.2% to 3.1% (p less than 0.0002), respectively. It was lowest for the patients in optimal condition (subgroup II) in both years, 0.8% versus 1.1%, and highest for reoperative patients, 5.3% versus 4.3%. In 1981, 58% of patients (503/870) were in the optimal group compared with 35% (292/828) in 1987 (p less than 0.0001). The last six years have seen a progressive trend in surgically treating older, sicker patients who have more complex disease, with a significant reduction in the best candidate group.(ABSTRACT TRUNCATED AT 400 WORDS). 