It has been apparent during the developmental phase of aortic valve surgery that further progress would come only when the aortic valve could be exposed for a sufficiently long period of time to allow for the proper evaluation of the pathological features and their definitive correction. In the past, partial correction with a high operative mortality has been obtained with the use of closed techniques or hurried procedures with the patient under hypothermia. With the advent of extracorporeal circulation with the use of a mechanical pump oxygenator, 12 patients with aortic stenosis and regurgitation have been operated on during the past three years. If the patient was fortunate enough to have primarily fibrous aortic stenosis which could be corrected within a relatively short period of time, such operations could be successfully performed with use of elective cardiac arrest with potassium or acetylcholine and retrograde coronary sinus perfusion. However, if the