A thallium stress test is a nuclear imaging study that shows how well blood flows to the heart muscle. It usually is combined with an exercise stress test on a treadmill or stationary bicycle. The test can help doctors determine the causes of chest pain, the level of exercise you can perform safely, the extent of any coronary artery damage from a heart attack, and the effectiveness of procedures done to improve circulation in coronary arteries.
A small amount of thallium, a radioactive substance, is injected when you reach your maximum level of exercise. Then you lie down while a "gamma" camera takes images of the thallium as it mixes with blood in the bloodstream, the coronary arteries and heart muscle cells. If any part of the heart muscle isn’t receiving a normal blood supply, there will be less than the normal amount of thallium in those cells.
After the first pictures are made, you lie quietly for two to three hours. Then other pictures are taken to show heart activity at rest.
If blood flow to your heart is normal at rest but not when the heart is stressed during exercise, the difference may be due to a blockage in one or more of the coronary arteries. If the test is abnormal during both exercise and rest, blood flow to the heart is limited. And if no thallium shows up in some part of the heart muscle, cells there are dead from a prior heart attack.
I discussed your question about thallium with Joseph Alpert, M.D., a cardiologist and chief of the department of medicine at the University of Arizona in Tucson. He explained that the amount of thallium given for the stress test is quite small and is rapidly eliminated from the body in urine. There is no danger to others, including children (as long as they do not come into contact with your urine). And you don’t need to do anything to help your body eliminate the thallium; it will be gone quickly on its own.
Andrew Weil, M.D.
More information on heart health.