I think it all depends upon what your specific problem is. From what I've read if you had an AVR with no comorbidities you are most likely not at enhanced risk. You might be interested in this article posted today: 'Stay on Angiotensin Drugs' Still the Message as Trials Begin
Any cardiac patient, whether you have surgery or not, is high risk. Ask your cardiac doctor and he/she will explain to you the risks cardiac and other conditions are considered high risk.