I could be wrong ,but I thought with a stress echo they just shoot for a target heart rate and once you reach that you jump off the treadmill and onto the exam table for the post exercise portion of the echo.
Typically if you have to wait for the results, they're not terrible ;)
I agree with the former post though about stress testing and max heart rate - though I am not personally familiar with a stress echo and I know they're a little different. Hope the news is good news.