Patients who undergo peripheral vascular surgery are at increased risk for postoperative cardiac events and are difficult to assess preoperatively because of limitations on their activity. We prospectively studied 176 consecutive eligible patients undergoing elective vascular surgery to determine the value in predicting a postoperative cardiac event of preoperative electrocardiographic monitoring to detect myocardial ischemia. Of the 176 patients, 32 (18 percent) had 75 episodes of monitored ischemic ST-segment depression preoperatively (of which 73 were asymptomatic), and 13 (7 percent) met strict criteria for major postoperative cardiac events, including 1 with a fatal myocardial infarction, 3 with nonfatal infarctions, 4 with unstable angina, and 5 with ischemic pulmonary edema. Of the 32 patients with ischemia before their operations, 12 had postoperative events (univariate relative risk, 54; 95 percent confidence interval, 7.2 to 400). Only 1 postoperative event occurred among 144 patients who did not have preoperative ischemia. The sensitivity of preoperative ischemia was 92 percent, the specificity 88 percent, the predictive value of a positive result 38 percent, and the predictive value of a negative result 99 percent. In multivariate analyses, preoperative ischemia was the most significant correlate of postoperative cardiac events and remained a statistically significant independent correlate even after we had controlled for all other preoperative factors (multivariate relative risk, 24.4; 95 percent confidence interval, 6.8 to 88). These preliminary data suggest that preoperative electrocardiographic monitoring to detect episodes of myocardial ischemia is a useful method for assessing cardiac risk in patients who undergo elective vascular surgery. In particular, the absence of ischemia during monitoring indicates a very low risk.