There is no controversy about the prosthetic replacement of the aortic valve in cases in which there is a disorder of function or cardiac failure, or in cases with a tight aortic stenosis, even if it appears to be well-tolerated clinically. It is especially critical in cases of aortic incompetence with marked cardiac enlargement, but the problems are not overwhelming. The indications for operation in very advanced cases with cardiac failure which is refractory, or in aged patients, are discussed.