This is a type of nuclear scanning test or myocardial perfusion (mi"o-KAR'de-al per-FU'zhun) imaging test. It shows how well blood flows to the heart muscle. It's usually done along with an exercise stress test on a treadmill or bicycle.

The thallium stress test is useful to determine:

- Extent of a coronary artery blockage

- Prognosis of patients who've suffered a heart attack

- Effectiveness of cardiac procedures done to improve circulation in coronary arteries

- Cause(s) of chest pain

- Level of exercise that a patient can safely perform

The first pictures are made shortly after the exercise, can be strenous or light, test and show blood flow to the heart during exercise. The heart is "stressed" during the exercise test -- thus the name "stress test." The patient then lies quietly for 2-3 hours and another series of pictures is made. These show blood flow to the heart muscle during rest.

- If the test is normal during both exercise and rest, then blood flow through the coronary arteries is normal. The coronary arteries supply blood to the heart muscle.

- If the test shows that perfusion (blood flow) is normal during rest but not during exercise (a perfusion defect), then the heart isn't getting enough blood when it must work harder than normal. This may be due to a blockage in one or more coronary arteries.

- If the test is abnormal during both exercise and rest, there's limited blood flow to that part of the heart at all times.

- If no thallium is seen in some part of the heart muscle, the cells in this part of the heart are dead from a prior heart attack. (They have become scar tissue.)

Sometimes you can't do an exercise test because you're too sick or have physical problems. In this case, a drug such as dipyridamole (di-pi-RID'ah-mol) or adenosine is given. This drug increases blood flow to the heart and thus "mimics" an exercise test. Then the thallium test is given.

Most people can raise their HDL (good cholesterol) levels by exercising, not smoking and staying at a healthy weight.