Mine was diagnosed at 4.0 almost 4 years ago and then went to 4.2 in a year. Now steady at 4.5 the last year and a half. Based on information from my local cardiologist and also from the head of cardiothorasic surgery at a university hospital who also reviews my scans, surgery is recommended at 5.0 cm (unless they see a rapid increase in readings). They explained to me that surgery is major and high risk, around 5% fatality rate, but depends on the hospital. Not having surgery before 5% the risk is down to well below 1%. They also told me that people who manage it (no heavy lifting, no strenuous exercise, keeping blood pressure low etc) have a low risk and as one of them said "you would go from something else totally unrelated".