The two main reasons for shortness of breath are from the heart and from the lungs. The changes you have in your arteries and valves may or may not be sufficient to produce the breathing problems you are describing. Some of it depends on how rapidly these changes have occurred. The lung function test and 6 minute walk will definitely tell you if the problem is related to your lungs. Without having more information it is hard to give the answers you are seeking. I am sure you will know much more after the lung tests and your next physician visit.
Sandi