Correlation of EKG Stress test and potential for heart attack

My EKG stress test revealed that my V3 ST depression was positive and flat from start of test to 90 BPM, moderate slope from 90 to 120 BPM (i.e., -0.9 ST depression at 120 BPM) and severe sloped from 120 BPM to end of test at 142 BPM (-3.8).  Can I infer a safe exercise level from these results?  I was told that while the condition is not life threatening if I exercise at low levels, I also inferred that there was significant risk of heart attack if I exercised at higher levels (125 to 135 BPM).  The angiogram revealed two blockages (90 and 75%) in a branch of the left main artery, and a single blockage in a branch of the right coronary artery (75%).  The cardiologist elected not to remove the blockages using angioplasty or a stent, but to try medications for a month and do another treadmill-EKG and nuclear.  Assuming there is no change in the results, is it possible that using angioplasty and a stent to remove the blockages (1, 2, or all 3) would change the EKG treadmill, which would reduce threat of a heart attack if I exercise at higher BPM levels.