What is a stress test for the heart and why is it important?

EKG during exercise: Ekg's are taken at rest and during exercise and recovery. Certain ekg abnormalities are suggestive of blocked arteries to the heart. If these changes occur, the test is positive and is stopped. If the predetermined heart rate is reached without abnormalites, the test is negative. If the goal heart rate is not achieved the test is non-diagnostic. It is a test for blockage of arteries to the heart.

ForAdvancedDisease: Promoted for detecting artery disease, but misses most disease; arteries expand, not narrow. ~75%, or more, narrowing required before stress tests, all forms, begin to detect any abnormalities. Nuclear (more expensive ; radiation) promoted as more sensitive. For all I have seen, a well done ekg exercise stress more sensitive ; accurate. I quit doing stress tests 1995; for better protection options.