The timing of surgery in chronic aortic regurgitation depends to a large extent on the operative results that may be expected in this type of valve disease. In 88 cases of chronic aortic regurgitation submitted to surgery there were 6 operative deaths (6.8%). Five years after operation the actuarial survival was 58% for the whole of the group and 68% for cases of rheumatic aortic regurgitation. Analysis of the causes of failures, late deaths, persistence or recurrence of severe impairment of activity, and of serious disturbances of ventricular rhythm, showed that the most important cause was myocardial dysfunction, which was responsible for two thirds of the bad results. Analysis of the late prognosis as a function of the various pre-operative parameters revealed the bad influence of cardiomegaly as measured by radiological examination (cardio-thoracic ratio and cineangiography) and of disturbances in left ventricular function. The actuarial survival curves showed very significant differences according to whether the cardiothoracic ratio was greater or smaller than 58%, and according to the amount of heart failure pre-operatively. Similarly, an end-diastolic volume index of 240 ml/m2 and an ejection fraction less than. 40 seemed to be serious findings. These facts, taken in conjunction with the natural history of this valve lesion, suggest that the indications for surgery should not only be symptomatic aortic regurgitation but also well tolerated regurgitation in which cardiomegaly, end-diastolic volume and/or the ejection fraction have reached a certain level.