Ascending thoracic aortic aneurysm (ATAA), an enlargement of the aorta near its exit from the heart, is largely harmless unless a vessel wall failure event occurs. A failure event, however, is life-threatening and would best be prevented by surgical intervention before the tissue fails. Surgical intervention, while effective, is also costly and dangerous, so the challenge to the biomedical engineer is to develop tools to help identify and quantify the risk to a specific patient based on available information. The question, at its core, is a mechanical one – will the stress exceed the strength? The problem is that, unlike a traditional design problem, the tissue can change itself over time, and we cannot readily measure properties (especially not failure properties) of a tissue while it is still in use by the body. The seminar will discuss the experimental and computational methods that we use to attack this problem.