Surreysue, when they see an inverted T wave, they start worrying about schemia (lack of O2 to the heart muscle that could have been caused by a small heart attack).
The stress EKG is used to see whether the inverted T wave shows up during exercise.
Yet, there are many people with "abnormal" EKG readings, but with perfect functional hearts. Ten healthy people will probably show four different EKG tracings at rest.
All the best