A nuclear stress test measures and images blood flow to your heart at rest and while your heart is working harder as a result of exertion or medication. It’s usually done if a blockage is suspected because of symptoms of chest discomfort or shortness of breath, or if other tests, even without symptoms, suggest to your doctor that this may be a possibility. The test provides images that can show areas of low blood flow through the heart as well as detect damaged heart muscle. It involves taking two sets of images of your heart – one while you’re at rest and another after you heart is stressed, either by exercise or medication. During the test, you’re given a radioactive isotope (EYE-so-tope) through a small IV, so this test does involve entering a vein just under your skin, usually in the upper extremity.