Yes, most certainly if a valve replacement is warranted, then you can undergo a redo surgery. There is nothing like gap between one valve replacement to another. If it is required within a month, then it should be done within a month and if it is required after 3-4 years as in your case, then it is fine. Every surgery has a definite risk in terms of complications and risk of life. In a redo aortic valve, the risk of life would stand some where between 3-5%. However, the risk quantification can be done after having full check up of the patient because so many factors decide the risks in these situations.