stress thallium test in delhi 09999446542 A thallium stress test is a nuclear imaging test that shows how well blood flows into your heart while you're exercising or at rest. This test is also called a cardiac or nuclear stress test. During the procedure, a liquid with a small amount of radioactivity called a radioisotope is administered into one of your veins. The radioisotope will flow through your bloodstream and end up in your heart. Once the radiation is in your heart, a special camera called a gamma camera can detect the radiation and reveal any issues your heart muscle is having.