A thallium stress test is a nuclear imaging procedure that indicates how well blood flows into the heart, while a person is exercising or at rest. This test is also called a cardiac or nuclear stress test that shows regions with poor blood flow or any damage in the heart. During the procedure, a liquid containing a minimal amount of radioactivity called a radioisotope is administered into veins. The radioisotope will flow via the bloodstream and finally reach up to the heart. Once the radiations reach the heart, a specially designed camera called a gamma camera can detect the radiation and discloses any problems the heart muscle is having.

A nuclear stress test is one of the various kinds of stress tests. The radiotracer used during the procedure helps the healthcare provider to find out the patient risk of a heart attack or any other cardiac event. This test is done using a Positron Emission Technology (PET) scanner or Single Photo Emission Computed Tomography (SPECT) scanner. A nuclear stress test is also called a Myocardial Perfusion Imaging (MPI) study, cardiac PET study or cardiac SPECT study.
Thallium stress test

Why It Is Done?

The doctor may recommend a thallium stress test for several reasons including:

  • If the healthcare provider suspect patient’s heart is not working effectively when it is under stress or while exercising
  • If the person has chest pain or aggravating angina
  • Previous history of heart attack
  • To monitor how well medications are working
  • To check whether a procedure or surgery was successful
  • To check whether the heart is functioning healthy enough to begin an exercise program

 The stress thallium test can show: 

  • The size of heart chambers
  • How well heart pumps - ventricular function
  • How efficiently coronary arteries supply blood to the heart- myocardial perfusion
  • If the heart muscle is damaged or scarred due to previous heart attacks

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A health care provider or a nurse inserts an intravenous line on the inside of the elbow. A radioisotope or radioactive tracers such as thallium or sestamibi is injected via the IV. The radioactive material marks the blood flow, and it is captured up by the gamma camera. The procedure involves an exercise and resting segment, and the heart muscle images are captured during both the segments. The patient will receive an injection before each segment.

Resting Segment

The patient is made to lie down on the exam table for 15 to 45 minutes while the radioactive material works its way via the body to the heart. The patient has to lie down on an exam table with arms above the head and a gamma camera above takes pictures.

Exercise Segment

In the exercise part of the test, the patient is made to walk on a treadmill. The doctor will ask the patient to start off slowly and progressively pick up the pace into a jog. The patient may require running on an incline to make it more effective and challenging.

If the patient is unable to go about with exercise, the doctor may give a medication that stimulates the heart and makes it beat rapidly, which resembles how the heart would be acting while exercising.

Blood pressure and heart rhythm are monitored while exercising, as soon as the heart starts working hard as it can, the patient is asked to get down off the treadmill. After 30 minutes, the patient has to lie down on an exam table again. The gamma camera then captures the images that show the flow of blood via the heart. The doctor will then compare these images with the set of resting images to find out how weak or strong the blood flow to the heart is.

How To Prepare For A Thallium Stress Test?

Before the procedure, the patient has to fast after midnight before the test or at least four hours prior to the test. Fasting may avert any chance of a patient falling sick during the exercise segment. Wear comfortable clothes and shoes for exercising.

Twenty-four hours before the test patient need to avoid all caffeinated beverages, including tea, coffee, soda, chocolate or any drinks that contain even a small amount of caffeine and pain relievers. Drinking caffeine can increase heart rate to a higher range than it normally would. It is important to inform the doctor about current medications that the patient is taking as some medications can interfere with the test.


Generally, most people tolerate well while doing the stress thallium test. The patient may feel a tickle as the medication that stimulates exercise is injected, followed by a warm feeling. While some patients may experience headaches, nausea, and rapid heartbeat.

The radioactive tracer will be eliminated from the body via the urine. Any complications arising due to radiative material being injected into the body is very rare.

Some of the rare complications from the test may include:

Irregular heartbeat

Increasing pain due to poor blood flow in the heart

Difficulty breathing


Variation in blood pressure

Skin rashes

Chest discomfort


Inform the scan technician if you experience any of these symptoms while doing the test.


The test results generally depend on the patient’s age, history of existing heart problems and other medical concerns.

Normal Results

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

Abnormal Results

Abnormal results may signify:

Reduced blood flow to the region of the heart is caused by the blockage of one or more arteries that supply the heart muscle.

Scarring of the heart muscle due to previous heart attack.

Any existing heart disease.

An enlarged heart.

The doctor may further suggest doing more tests to determine if the patient is having any heart problems. The doctor will develop a treatment plan based on the results.