@dalehopper5653 When to have surgery is a tradeoff between the risk of the aneurysm dissecting and the risks of open heart surgery. Many thoracic surgeons use 5.5 cm as the size to do surgery, but at some high volume surgery centers they use 5.0 cm. As Moonboy notes there are also other factors your surgeon takes into consideration to determine when to do surgery. If you are concerned about what size to have surgery you may want to get a second opinion.