Thallium stress test is a nuclear imaging method that shows how well blood flows into the heart muscle, both at rest and during activity.

This test is done at a medical center. The test is done in two parts:

• Part 1: You will walk on a treadmill or be given a medicine called a vasodilator to increase your heart rate. You will be given the drug if your doctor does not think exercise is safe for you or if you have joint problems that may make doing so difficult.
• Part 2: The health care provider will inject a radioactive substance into one of your veins and then take pictures of your heart.

The radioactive material may be thallium or sestamibi. (If sestamibi is used, it's called a "sestamibi stress test.") This substance travels through your bloodstream into the heart muscle.

Next, you will be asked to lie down on a table under a special camera that scans the heart. A computer creates pictures of the heart by tracking how the radioactive material moves through the area.

The first pictures are taken shortly after you get off the treadmill or are given the vasodilator drug. These images show how blood flows to the heart during exercise. This is the part most commonly referred to as the "stress test," because it is the most challenging for your heart.

After lying quietly for a few hours, you'll have more pictures of the heart taken. These images show blood flow through your heart during rest.

The entire test can take about 4 hours. You will usually be given a long break in between scans and allowed to have caffeine-free lunch or a snack at a nearby cafeteria.

You should wear comfortable clothes and shoes with non-skid soles. You will probably be asked not to eat or drink anything after midnight, except for a few sips of water if you need to take medicines.

You will need to avoid caffeine for 24 hours before the test. This includes caffeinated beverages such as tea, coffee, and sodas, as well as chocolates, and certain pain relievers.

Your doctor will tell you if you need to stop taking any medicines before the test. Medications used to treat asthma and angina may interfere with test results. Never stop taking any medicine without first talking to your doctor.

Some people feel fatigue, muscle cramps in the legs or feet, shortness of breath, or chest pain during the treadmill test.

If you are given the vasodilator drug, you may feel a sting as the medication is injected, followed by a feeling of warmth. Some patients also have a headache, nausea, and a feeling that their heart is racing.

If any of the symptoms listed above appear during your test, let the lab personnel know immediately.

Your doctor may order this test to determine:

• How well your heart responds to exercise
• The cause of new chest pain or worsening angina
• What you can expect after you have had a heart attack
• How well a treatment done to improve blood flow in your coronary arteries is working

A normal result means blood flow through the coronary arteries is normal.

Note: Normal value ranges may vary slightly among different medical centers. Talk to your doctor about the meaning of your specific test results.

Abnormal results may be due to:

• Reduced blood flow to a part of the heart; the most likely cause is a significant blockage of a coronary artery.
• Scarring of the heart muscle due to a previous heart attack

Complications are rare but may include:

• Arrhythmias
• Increased angina pain during the test
• Difficulty breathing or asthma-like reactions
• Extreme swings in blood pressure
• Skin rashes

Your health care provider will explain the risks before the test.

Breast tissue in women and non-heart tissues such as the diaphragm can sometimes cause false positive test results. Further tests may need to be done to confirm the results. These may include a a stress echocardiogram or a cardiac catheterization.

Udelson JE, Dilsizian V, Bonow RO. Nuclear Cardiology. In: Libby P, Bonow RO, Mann DL, Zipes DP, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 8th ed. St. Louis, Mo: WB Saunders; 2007: chap. 16.