The thallium stress test is similar to a regular stress test in that your heartbeat is recorded while you walk on a treadmill or ride a stationary bike, to a maximum exercise level. See EXERCISE STRESS TEST for more information. In addition, this test involves injecting an intravenous (IV) tracer, then stopping the exercise and immediately scanning the heart. Pictures are taken immediately after exercise and then several hours later in order to determine how well the blood flows to each region of the heart muscle.