What Is a Nuclear Stress Test?

What to expect when undergoing this test

A nuclear stress test can help your doctor find a heart problem. Sometimes these problems can only be seen when you are exercising.

When you exercise, your heart is said to be under stress. This is why it is called a "stress test."

The nuclear stress test is most often used to look for blockages. Blockages may happen when you have coronary artery disease.

The nuclear stress test can also help your healthcare provider understand how severe the blockages are.

This article discusses the nuclear stress test, its purpose, and its potential risks. It will also help you prepare for the test and know what to expect during and after testing.

what to expect during a nuclear stress test

Verywell / Emily Roberts

Purpose of the Nuclear Stress Test

Your doctor may order this test if you have unexplained symptoms like:

These symptoms could be a sign of coronary artery disease. This is a condition where fatty deposits form in the blood vessels that supply your heart. 

The test can find blockages. It can also help your healthcare provider judge how severe the blockages are.

If you already have a diagnosis of coronary artery disease, your doctor may still order this test. The results can help your doctor develop a treatment plan.

If you are being treated for coronary artery disease, the test can also help your doctor understand how well your treatment is working. It will also help your doctor decide what kinds of daily activities and exercise you should be doing.

The nuclear stress test is non-invasive. This means it doesn't involve inserting medical instruments into the body. This test is thought to be the most accurate non-invasive way to diagnose coronary artery blockages.

In many cases, a nuclear stress test can make cardiac catheterization unnecessary. This is a procedure where a tube called a catheter is inserted into a blood vessel in the heart.

Recap

The nuclear stress test is used to find blockages in the coronary arteries. Your doctor may order this test if you have unexplained symptoms like chest pain and shortness of breath.

What the Test is Looking For

The nuclear stress test creates two images. The first shows how blood flows to the heart during rest. The second shows blood flow during exercise.

The test can find:

  • The presence, location, and size of a prior heart attack
  • The presence, location, and size of blockages that are serious enough to affect blood flow during exercise

A normal test result will show blood evenly distributed to the heart in both images.

If both images show a fixed patch of poor blood flow, that means there has been a prior heart attack.

If an area of poor blood flow can be seen on the exercise image but not on the rest image, there is probably a blockage in one of the coronary arteries. The blockage is causing a temporary drop in blood flow.

Recap

The nuclear stress test shows how blood is flowing to your heart. The test can find blockages and identify damage from a prior heart attack.

The Radioactive Tracer

The nuclear stress test uses a radioactive tracer to create a picture. This is a very small amount of radioactive material. It is delivered through an intravenous (IV) line. 

The tracer commonly used today is technetium-99 (Tc-99). This tracer provides clearer images than the tracers used in the past. It also creates less radiation exposure.

Rest and Exercise Images

Most labs do one-day nuclear stress testing. The test can also be done over a two-day period. One day testing, however, is generally more convenient for the patient.

The resting image is captured first. For the resting image, the dose of Tc-99 is small. The image is captured with a gamma camera. This is a special camera that is used to scan the chest.

The stress image is captured a few hours later. For the stress image, the Tc-99 dose is much larger. It is injected during peak exercise. The exercise is usually done on a treadmill or stationary bicycle.

For both images, the gamma scan is done 15 to 60 minutes after the tracer is injected.

In People Who Cannot Exercise

Exercise stress testing is the prefered way to do a nuclear stress test. Some people, however, can't do the type of exercise required for this test. They may have physical limitations that make exercise difficult or impossible.

These patients may undergo pharmacologic stress testing instead of exercise stress testing. This is done with drugs that cause the same type of stress as exercise.

The types of drugs used may include:

  • Vasodilators such as Adenocard (adenosine) or Persantine (dipyridamole)
  • Inotropic drugs, usually Dobutrex (dobutamine)

Vasodilators are usually preferred. These are medications that dilate or open the blood vessels. Your healthcare provider will choose the best drug for your case if exercise is not an option.

Recap

The nuclear stress test captures blood flow images while you are at rest and while you are exercising. If you can't exercise, you'll be given a drug that simulates what happens in your heart during exercise.

Risks and Contraindications of a Nuclear Stress Test

When performed by experienced health care providers, the nuclear stress test is very safe. Still, there are known risks. These include:

  • Cardiac arrhythmias: Exercise-induced heart arrhythmias may occur. This is when your heart beats too fast, too slow, or irregularly. Arrhythmias are rarely dangerous. They almost always disappear when the exercise stops. While arrhythmias are considered a risk of stress testing, their presence can also help with diagnosis. Finally, if potentially dangerous arrhythmias happen during modest exercise, it is better to find out about them in a controlled setting than on the street.
  • Chest pain, dizziness, or other symptoms: In people with serious coronary artery disease, modest exercise can cause symptoms of cardiac ischemia. This is insufficient blood flow to the heart muscle. This is considered a risk of this test. However, it can also be useful to see exercise-related symptoms during the test. They can help the healthcare provider understand if the symptoms are caused by coronary artery disease. In fact, in people who are being assessed for exercise-related symptoms, one of the goals is to reproduce the symptoms.
  • Allergic reaction: Some people may have an allergic reaction to the radioactive tracer. This is very rare.
  • Heart attack: In a person with a critical blockage, exercise might produce a heart attack. This is also very rare.

Life-threatening complications are very uncommon. They are estimated to occur only in 1 out of every 10,000 exercise tests.

Recap

The nuclear stress test is generally very safe. It may cause side effects like cardiac arrhythmias or chest pain. In rare cases an allergic reaction or heart attack may happen.

Some people should not do nuclear stress testing. These include people with:

During a typical nuclear stress test, you are exposed to 11 millisieverts of radiation. This is about three times the dose of radiation you get from living a normal life for one year.

This is considered a small amount. By itself, it should not increase your lifetime risk of cancer by any measurable amount.

Recap

There are some conditions that may exclude you from being able to have the test, like a very recent heart attack or uncontrolled heart failure.

Before Your Nuclear Stress Test

It is normal to have some anxiety about this test. These details may help you prepare.

Timing and Location

Most nuclear stress tests are performed in a hospital outpatient area.

You will probably be asked to show up at least 30 minutes before the scheduled test. You can expect to be there for at least four hours.

What to Wear

Since you will be exercising, bring comfortable, loose-fitting clothing. Make sure to bring shoes that fit well. Many people bring gym clothes and walking or running shoes. Most testing facilities will provide a place to change.

Food and Drink

You will be asked to avoid food, drink, and smoking for 4 to 6 hours before your test. Avoid caffeine for at least 24 hours before the test.

Medications

If you take prescription medications, ask your healthcare provider which medications you should take on the day of testing, and which you should not take.

If you have diabetes, you'll be given instructions on how to take your medications on the day of the test.

Avoid taking any over-the-counter medications before the test unless you clear it first with your healthcare provider.

Cost and Health Insurance

The nuclear stress test is relatively expensive. The cost varies from place to place. It may also vary depending on what type of insurance you have.

Most medical insurance covers the nuclear stress test if a qualified cardiologist says you need it. To be sure, you may want to check with your insurance company before your test.

What to Bring

You will probably have a few hours of downtime during the testing process. Bring a book or something else to help fill the time.

Other Considerations

If possible, bring a family member or a friend. This person can help you pass the time and offer support if you expect to get the results on the day of testing.

Recap

Most nuclear stress tests are done in hospital outpatient areas. Wear comfortable clothing and shoes. Follow your doctor's instruction for food and medications before your test. It may be helpful to bring a close friend or family member to support you when you get your test results.

During Your Nuclear Stress Test

Knowing what to expect before and during the test can help ease any anxiety you may have.

Pre-Test

After you arrive for testing you will be interviewed by someone on your healthcare team. This person will ask if your symptoms or medical condition has changed since you last saw your doctor. You will also undergo a quick physical exam.

Your team will let you know what to expect during the test. You will also be given a chance to ask questions.

Throughout the Test

The testing should be supervised by a healthcare provider. The provider should let you know who they are.

If you are doing a one-day test, the resting image is done first. The exercise part will be done later the same day. For a two-day test, the exercise part is usually done on the first day. The resting part is done on the second.

During the resting test, a technician will insert an IV line into one of your veins. A small amount of tracer will be injected.

After about 20 minutes, you will lie down under a gamma camera. You will need to keep your arms above your head and lie still.

It will take another 15 to 20 minutes to make the image. The image will show how the blood is flowing to your heart.

For the exercise test, a technician will place electrodes on your chest. This is so an electrocardiogram (ECG) can be recorded during exercise. This test measures the electrical rhythm of your heart. 

As the test begins, you will walk on a treadmill or pedal a stationary bike at a very slow pace. The level of exercise will increase every three minutes. The exercise will stop when one of these things happens:

  • You become fatigued
  • You develop symptoms
  • You reach your target heart rate

When you have reached the maximum level of exercise, the tracer will be injected into your IV. At that point, you will stop exercising.

Your ECG and vital signs will be monitored throughout the exercise and recovery periods. The exercise itself usually lasts for no more than 6 to 12 minutes.

Twenty to 30 minutes after you've finished exercising, you will lie under the gamma camera again. You will be asked to keep your arms above your head. The exercise cardiac image takes about 20 minutes to make.

Recap

In one-day tests, the resting test is usually done first. The exercise portion is done later the same day. The exercise portion usually takes place on a treadmill or stationary bike.

After your Nuclear Stress Test

Most people are told to resume their normal routine immediately after the test. This includes meals, medications, and other activities.

The amount of radiation you receive during this test is considered very small. There are no special precautions you will need to take afterwards.

How and when you get your results depends on the testing center. Most laboratories will give you an overview of the results right away. If the test finds concerning problems, you'll be given advice on what to do next.

If there are no obvious problems, you probably won't get the formal results until a cardiologist looks at the images. In this case, you'll get your results from your referring healthcare provider. Afterwards, you'll discuss what if anything should be done next.

Managing Side Effects

You may have some fatigue from the exercise. Otherwise, you should expect no side effects. If you have any unusual symptoms after the test, call your healthcare provider.

Recap

You should be able to return to normal activities right after your test. Other than fatigue, most people do not experience side effects.

Interpreting the Results of a Nuclear Stress Test

The interpretation of the results is different for everyone. You'll need to discuss the results with your healthcare provider.

In general, though, the results of a nuclear stress test fall into three categories.

1. Both the resting and exercise cardiac images are normal

This result suggests:

  • There is no detectable permanent heart damage from a prior heart attack
  • No part of the heart is deprived of blood flow during exercise

This result strongly suggests that there are no significant coronary artery blockages.

Your healthcare provider will discuss the next steps with you. If your test is normal, you may not need more cardiac testing.

If there is strong evidence of coronary artery disease, your healthcare provider will likely recommend immediate medical treatment. The goal will be to relieve symptoms and slow the progression of the disease.

Your healthcare provider may discuss the possibility of cardiac catheterization if:

  • Your symptoms are severe
  • The risk of an early heart attack appears to be high

2. The resting cardiac image is abnormal

The resting cardiac scan may show an area where blood is not flowing normally to part of the heart. This indicates you've had a prior heart attack. The heart attack caused permanent heart muscle damage.

3. The exercise cardiac scan is abnormal, but the resting image is normal

Together, these results indicate there is a significant blockage in a coronary artery:

  • The heart is getting normal flow at rest
  • The heart is not getting the right amount of blood flow during exercise

Different parts of the heart muscle may display any of these general findings.

For example, a person could have a “permanent” defect in one part of the heart muscle. This indicates a heart attack has occurred. They may also have a “reversible” defect in another portion of heart muscle. This indicates a blockage but no permanent damage.

Recap

The test results will fall into one of three categories:

  • Normal results will show no prior heart attack or evidence of blockage
  • Abnormal resting results may show evidence of a prior heart attack
  • Abnormal cardiac results with normal resting results indicate there is a blockage in the coronary artery

Summary

A nuclear stress test is used to find heart problems. The test uses a small amount of radioactive material to record blood flow to your heart. The test is done during rest and exercise.

A nuclear stress test can find evidence of a prior heart attack. It can also find blockages. It can help your doctor understand how severe the blockages are.

If you can't exercise, a drug can be used to create the same type of stress on your heart. 

The nuclear stress test is generally very safe. There are some risks, like cardiac arrhythmias, chest pain, and, in rare cases, heart attack. The amount of radiation used is very small and does not increase your lifetime risk of cancer.

Most tests are done in hospital outpatient areas. They may be be done in one day or over the course of two. Most people can return to normal activities immediately afterwards. There are usually no side effects.

Results may indicate coronary artery disease, blockages, or previous heart attack. Your doctor will discuss the next steps with you, depending on the results. 

A Word From Verywell

Nuclear stress is a noninvasive method of looking for blockages in the coronary arteries. It is generally safe and effective.

A nuclear stress test can help your doctor understand if a blockage is causing your chest pain. It can also help identify heart damage that might be permanent.

This kind of testing has been proven helpful in diagnosing coronary artery disease. It can also help guide treatment.

Frequently Asked Questions

  • Can I take my regular medications before a nuclear stress test?

    Not unless your healthcare provider okays it. You may need to stop taking certain medications prior to the test. For instance, your healthcare provider may tell you not to take beta blockers, nitroglycerin, or heart medications for 24 hours before the test. You may also need to stop aspirin or blood thinners and asthma medications 48 hours before. Diabetes medication may also be restricted. Review all your medications with your healthcare provider beforehand.

  • Is the radiation in a nuclear stress test safe?

    The dosage should be safe. However, because there is direct exposure to radiation, there is a risk of cancer for anyone who undergoes a nuclear stress test. The American Heart Association and other organizations have created guidelines to help healthcare providers determine if the test is medically necessary, which means that the risk of cancer is outweighed by the benefit you can gain from having a potential heart problem properly diagnosed.

  • How long will radioactivity from a nuclear stress test stay in my system?

    Within a day, the radiotracer will lose its radioactivity through natural decay. You should pass it via urine or stool, but drinking water can help wash it out.

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8 Sources
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  1. American Heart Association. Myocardial perfusion imaging (MPI) test.

  2. Henzlova MJ, Duvall WL, Einstein AJ, Travin MI, Verberne HJ. ASNC imaging guidelines for SPECT nuclear cardiology procedures: stress, protocols, and tracers. J Nucl Cardiol. 2016;23(3):606-39. doi:10.1007/s12350-015-0387-x

  3. Wolk MJ, Bailey SR, Doherty JU, et al. ACCF/AHA/ASE/ASNC/HFSA/HRS/SCAI/SCCT/SCMR/STS 2013 multimodality appropriate use criteria for the detection and risk assessment of stable ischemic heart disease: a report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons. J Card Fail. 2014;20(2):65-90. doi:10.1016/j.cardfail.2013.12.002

  4. Harrison SD, Harrison MA, Duvall WL. Stress myocardial perfusion imaging in the emergency department--new techniques for speed and diagnostic accuracyCurr Cardiol Rev. 2012;8(2):116–122. doi:10.2174/157340312801784916

  5. American Heart Association. Cardiac catheterization.

  6. Cleveland Clinic. Pharmacological nuclear stress test.

  7. Pena M, Jakob M, Cohen G, et al. Reduction in radiation exposure through a stress test algorithm in an emergency department observation unit. WestJEM. 2016;17(2):97-103. doi:10.5811/2Fwestjem.2015.12.27895

  8. American College of Radiology. Cardiac nuclear medicine.