I had this today. It felt like I was climbing out of thr grand canyon. I made it and my heart rate was 135 when I finished. They inject tracer in to your arm and take pictures of your heart and then after that you go on the tread mill up hill and speed it up at differnt times and do a ekg at the same time, then after that they inject more tracer and take more pictures of my heart. This is to see if I have any blockage in my arteries to my heart. My doctor wanted to do this cause I developed a blood clot in my lung in June. I am glad I have been going to the gym on the tread mill every other day or I could not have done this test. I will see the Doctor on Monday and see if all is OK. What an experience, today.