Nuclear cardiology is useful in patients with chest discomfort to see if the discomfort comes from lack of blood flow to the heart muscle caused by narrowed or blocked heart arteries . A nuclear stress test uses radioactive dye and an imaging machine to create pictures showing the blood flow to your heart. The test measures blood flow while you are at rest and are exerting yourself, showing areas with poor blood flow or damage in your heart. The test can help better determine your risk of a heart attack or other cardiac event if your doctor knows or suspects that you have coronary artery disease.