The aim of this study was to assess the efficiency of exercise tests in identifying ischaemia in the territories supplied by the three main coronary arteries. We prospectively analysed 578 patients with single vessel coronary disease (> 50% stenosis in one vessel and completely normal other vessels). Patients with single vessel coronary artery disease were divided into three groups: patients with significant left anterior coronary artery disease (group 1, n = 234); patients with significant right coronary artery disease (group 2, n = 201); patients with significant left circumflex disease (group 3, n = 143). Our study, which is the largest prospective study of patients with angiographically documented single vessel coronary artery disease, suggests that the exercise electrocardiogram is a poor predictor of circumflex coronary artery ischaemia. In addition, the site of ST depression identified from the electrocardiogram was a poor predictor of the site of myocardial ischaemia. No single lead could distinguish between the three groups and the location of coronary stenosis could not be predicted by location of ST depression.