Emergency aortocoronary bypass operations were performed in 20 patients. In 12 they were done in the preinfarction stage, and all but one survived with excellent late results. In eight patients the operation was done in the acute phase of myocardial infarction; one died in the immediate postoperative period. Seven survivors have been observed from 6 to 12 months. Four have had complete relief of angina and have returned to normal activities. Two had initial improvement, but during the second and third postoperative months began complaining of exertional angina. One patient who developed a postoperative infarct continues to have pain at rest. Aortocoronary bypass improves angina and prevents infarction in selected cases with preinfarction angina. Patients in the acute phase of myocardial infarction can tolerate myocardial revascularization; the clinical course of these patients is favorable if adequate revascularization is accomplished.