The doctor will usually conduct an electrocardiogram while the patient is lying down and at rest. EKG data recorded during a stress test, however, shows heart activity while exercising. As the patient works harder, the heart responds to additional demands from the muscles or limitations on breathing and available oxygen. This may reveal heart muscle issues.

SerafinoMozzo / Getty Images
This site offers information designed for educational purposes only. You should not rely on any information on this site as a substitute for professional medical advice, diagnosis, treatment, or as a substitute for, professional counseling care, advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other healthcare professional.