What Causes The Requirement Of An Aortic Valve Replacement?

I had an aortic valve replaced because it wasn't opening enough. I never had any problems when I was younger. After returning from Viet Nam as I aged I lost my stamina to where I couldn't walk very far without being worn out. After a ultrasound it was determined that my valve needed to be replaced. The diagnosis was that it was genetic. Could my condition have been caused by agent orange exposure instead of being genetic ?