What is a thallium stress test?

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.

Your doctor may order a thallium test for a variety of reasons, including:

  • if they suspect your heart isn’t getting enough blood flow when it’s under stress — for example, when you exercise
  • if you have chest pain or worsening angina
  • if you’ve had a previous heart attack
  • to check how well medications are working
  • to determine whether a procedure or surgery was successful
  • to determine whether your heart is healthy enough to start an exercise program

The thallium stress test can show:

  • the size of your heart chambers
  • how effectively your heart pumps —that is, its ventricular function
  • how well your coronary arteries supply your heart with blood, known as myocardial perfusion
  • if your heart muscle is damaged or scarred from previous heart attacks

The test must be done at a hospital, medical center, or doctor’s office. A nurse or healthcare professional inserts an intravenous (IV) line, usually on the inside of your elbow. A radioisotope or radiopharmaceutical medication, such as thallium or sestamibi, is injected through the IV.

The radioactive material marks your blood flow and is picked up by the gamma camera.

The test includes an exercise and resting portion, and your heart is photographed during both. The doctor administering your test will determine the order that these tests are performed in. You’ll receive an injection of the medication before each portion.

Resting portion

During this part of the test, you lie down for 15 to 45 minutes while the radioactive material works its way through your body to your heart. You then lie down on an exam table with your arms above your head, and a gamma camera above you takes pictures.

Exercise portion

In the exercise portion of the test, you walk on a treadmill or pedal an exercise bicycle. Most likely, your doctor will ask you to start slowly and progressively pick up the pace into a jog. You may need to run on an incline to make it more challenging.

If you’re unable to exercise, your doctor will give you a medication that stimulates your heart and makes it beat faster. This simulates how your heart would act during exercise.

Your blood pressure and heart rhythm are monitored while you exercise. Once your heart is working as hard as it can, you’ll get off the treadmill. After about 30 minutes, you’ll lie down on an exam table again.

The gamma camera then records pictures that show the flow of blood through your heart. Your doctor will compare these pictures with the set of resting images to evaluate how weak or strong the blood flow to your heart is.

You’ll probably need to fast after midnight the night before the test or at least four hours before the test. Fasting can prevent getting sick during the exercise portion. Wear comfortable clothes and shoes for exercising.

Twenty-four hours before the test, you’ll need to avoid all caffeine, including tea, soda, coffee, chocolate — even decaffeinated coffee and drinks, which have small amounts of caffeine — and certain pain relievers. Drinking caffeine can cause your heart rate to be higher than it normally would be.

Your doctor will need to know all medications that you’re taking. This is because some medications — like ones that treat asthma — can interfere with your test results. Your doctor will also want to know if you’ve taken any erectile dysfunction medication including sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra) 24 hours before the test.

Most people tolerate the thallium stress test very well. You may feel a sting as the medication that simulates exercise is injected, followed by a warm feeling. Some people may experience headache, nausea, and a racing heart.

The radioactive material will leave your body through your urine. Complications from the radioactive material injected into your body are very rare.

Rare complications from the test may include:

  • arrhythmia, or irregular heart beat
  • increased angina, or pain from poor blood flow in your heart
  • difficulty breathing
  • asthma-like symptoms
  • large swings in blood pressure
  • skin rashes
  • shortness of breath
  • chest discomfort
  • dizziness
  • heart palpitations, or an irregular heart beat

Alert the test administrator if you experience any of these symptoms during your test.

Results depend on the reason for the test, how old you are, your history of heart problems, and other medical issues.

Normal results

A normal result means blood flowing through the coronary arteries in your heart is normal.

Abnormal results

Abnormal results may indicate:

  • reduced blood flow to part of your heart caused by narrowing or blockage of one or more arteries that supply your heart muscle
  • scarring of your heart muscle due to a previous heart attack
  • heart disease
  • a too-large heart, indicating other heart complications

Your doctor may need to order more tests to determine if you have a heart condition. Your doctor will develop a treatment plan specifically for you, based on the results of this test.