Nuclear stress tests are advanced diagnostic tools that provide pictures of blood circulation in the heart. The exam typically lasts around two hours or more. At the start of the test, a technician will use an IV to inject a radioactive dye, known as a radionuclide, into your veins. After waiting several minutes for your heart to absorb the dye, the technician will take images of your heart at rest.

During an exercise stress test, you’ll likely walk on a treadmill, use a stationary bike or take a vasodilator to simulate exercise. Once you’ve reached your peak heart rate, you’ll receive another injection of the dye. Afterward, the technician will take more pictures of your heart. Your doctor will compare these before and after images to examine your circulation and heart health.

Potential nuclear stress test side effects include shortness of breath during exercise, an allergic reaction to the dye or chest pain. You can take precautions after a nuclear stress test — such as drinking enough water to flush the dye from your system — to ensure no serious side effects develop.