The diagnostic accuracy of using electrocardiographic findings to identify affected vessels in cases of myocardial infarction and angina pectoris treated by percutaneous transluminal coronary angioplasty was assessed. From the anterior wall leads, ST segment elevation in leads I and aV(L) showed diagnostic accuracy (sensitivity, specificity and positive predictive value) in identifying proximal lesions of the left anterior descending coronary artery of 89%, 58% and 62%, and the diagnostic accuracy of the QS wave in V(1) was 62%, 83% and 72%, respectively. For the posterior wall leads, the corresponding values for the diagnosis of affected vessels based on R/S>1 in V(1) for the left circumflex coronary artery were 50%, 89% and 60%, respectively. The inferior wall leads with ST segment elevation in leads II, III and aV(F), and ST segment depression in aV(L), showed diagnostic accuracy for the right coronary artery of 90%, 90% and 92%, respectively. Bifurcation of the first diagonal branch, dominance of the posterior descending branch, the normal subtypes of the coronary artery and the occurrence of spontaneous recanalization may have influenced the accuracy of diagnosis. Adding a high lateral wall lead one intercostal space above V(4) and a posterior wall lead located one intercostal space below V(6) appeared to increase the diagnostic accuracy of detecting the coronary artery lesions responsible for myocardial ischemia.