We have studied clinical and ECG stress features of 119 patients with left main disease and 113 matched patients with three vessels coronary disease. Clinical features and ECG stress test do not differentiate the two groups as a whole. Exercise time duration was shorter, ST criteria were more positive, and peak heart rate was lower in the subgroups of patients with left main and involvement of a right dominant coronary artery. However due to a large overlap these criteria do not seem to be clinically useful. In conclusion, in an individual patient angina and stress ECG criteria do not differentiate the patients with left main from those with three vessels coronary artery disease.