I am female, 71, with type 2 diabetes, stage 4 kidney failure and obstructive sleep apnea. what would the prognosis of aortic valve replacement?

Reasonable: What condition of aortic valve do you have? If you have severe symptomatic aortic stenosis, aortic valve replacement is the only solution. Most people would have some comorbidities, so your other medical conditions are not a contraindication for surgery. If the risk of surgery is deemed probihitiveby the surgeon, there is a new procedure called 'tavr' which may be beneficial.

Depends! : It depends on the cardiac function and the indication for replacement. Your comprbidities definitely put at higher risk and the risk depends on how severe they are. It is a major surgery but with the use of experienced staff, most people do well.

Depends: Depends on many factors. Get expert opinions from your cardiologist and cardiac surgeon.