It's always confusing when we don't know the language, right? Do you have a follow up with the cardiologist to go over the results? I believe that supine and prone actually refers to the position you were in during the test. Were you laying down for the test and face down? I believe the prone position is known for greater sensitivity and that shows in the report that they saw more with prone images. It says larger but not 'how large'. You'll need to get information regarding that defect. It may mean you had an MI at some point but I would not bet your lunch on that answer and you need to get that information from the doctor. Were you or have you had chest pain? Again, I would definitely really only take your doctor's answer regarding this for sure, but your summed stress score of 3 indicates mild ischemia. Having 0 at rest is very good.
When do you follow up with your doctor?
Here's some basic info on stress tests. https://www.mayoclinic.org/tests-procedures/nuclear-stress-test/about/pac-20385231