We evaluated relations with operative results of emergency aortocoronary bypass grafting to severity of residual stenotic lesion after surgery in patients with impending myocardial infarction or acute myocardial infarction. Mortality in patients with residual stenotic lesion whose score more than 15 is 66%. Mortality in patients with residual stenotic lesion whose score less than 15 is 5%, excluding patients died with noncardiac cause. Four of 6 patients (66%) with residual stenotic lesion whose score more than 5 have residual angina after the operation. None of fourteen patients with residual stenotic lesion whose score less than 5 has residual angina after the operation. In theory, we could save their lives with only one graft in 76% patients and cure their angina with less than 2 grafts in 72% patients. These grafts are key grafts.