Cardiac risk in vascular surgery. The oral dipyridamole-thallium stress test. The value of the oral dipyridamole-thallium stress test in identifying patients at high risk of myocardial infarction after vascular procedures has not been documented. We studied prospectively 46 patients who underwent an oral dipyridamole-thallium stress test before undergoing vascular operations. Twenty patients (43%) had a positive test result, defined by a thallium defect with reperfusion, while 26 patients had a negative test result. Myocardial infarctions were documented postoperatively in 5 (25%) of 20 of the group with positive results and 1 (4%) of 26 of the group with negative results. Three of the six myocardial infarctions were clinical; all three were in the group with positive results. No correlation was identified between dipyridamole-thallium stress test results and clinical cardiac history. A positive dipyridamole-thallium stress test result is a more sensitive predictor of postoperative myocardial infarction than ejection fraction or history of coronary artery disease. The oral dipyridamole-thallium stress test is as useful as the intravenous test in this setting. 