Coronary artery disease is the cause of death in most patients who have transient ischemic attacks or stroke. Evaluation for this condition is not routinely performed in such patients, and no prospective studies have been reported. We prospectively examined 50 consecutive patients with transient ischemic attacks or mild stroke to determine the prevalence and importance of coronary artery disease. All patients were examined by a cardiologist and underwent both exercise thallium-201 scintigraphy and exercise radionuclide ventriculography. Sixteen patients were suspected to have coronary artery disease on the basis of clinical evaluation. In 15 of these the was confirmed by the nuclear scans. The remaining 34 patients had no clinical evidence of heart disease, yet 14 had abnormal cardiac scans. Twenty of 22 patients with abnormal scans who underwent cardiac catheterization had significant coronary artery disease or a cardiomyopathy. The discovery of heart disease altered clinical management in 13 patients. Overall, 29 of 50 patients had significant coronary artery disease, compared with a 7% prevalence of the condition in other patients of similar age at the same institution.