The risk associated with surgical revascularization for unstable anginais critically dependent upon the clinical presentation of the patient. Forthis study, between January 1982 and December 1987, clinical, angiographic,operative and hospital outcome data were collected prospectively for 6539patients undergoing surgery for unstable angina. Urgent surgery wasperformed in 1523 patients (23.3%), while 5016 (76.7%) underwentsemielective revascularization. The mean age was 58.9 +/- 9.2 years and 805patients (12.3%) were aged 70 years or above. The male:female ratio was3.6:1. Depressed left ventricular function (left ventricular ejectionfraction less than 40%) was present in 27.2% of the population.Preoperative myocardial infarction (within 30 days of surgery) had occurredin 588 patients (9.0%). Operative mortality was 4.6% (301 deaths). Stepwiselogistic regression analysis was performed to determine the independentpredictors of operative mortality. The following variables were selected indescending order: urgent surgery (P less than 0.001), coronary reoperation(P less than 0.001), depressed left ventricular (P less than 0.001), femalegender (P less than 0.001), increasing age (P less than 0.001), left mainstenosis (P = 0.002), and preoperative myocardial infarction (P less than0.001). Predicted operative mortality varied between 0.5 +/- 0.3% and 82.6+/- 12.7%. The most important determinant for patients with a preoperativemyocardial infarction was left ventricular dysfunction, whereas urgentsurgery for unstable angina was the most important risk variable in thosewithout preoperative necrosis.