Quick answer: A nuclear stress test (myocardial perfusion imaging) uses a small amount of a harmless radioactive tracer and a special camera to show how well blood reaches your heart muscle, both at rest and when your heart is working harder. In Singapore it is arranged by a cardiologist, often at centres such as the National Heart Centre Singapore, to help find areas of the heart that may not be getting enough blood.
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In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.
If you have had chest pain, breathlessness or a known heart problem, your cardiologist may recommend a nuclear stress test. It combines a “stress” on the heart with heart imaging to look for reduced blood flow through narrowed heart arteries. This guide explains what the test is, why it is done, how to prepare, and what to expect on the day, written for patients in Singapore. It is general information and not a substitute for advice from your own doctor.
What a nuclear stress test is
A nuclear stress test, also called myocardial perfusion imaging, is a heart scan that uses a small amount of a harmless radioactive tracer and a special camera to show how well blood reaches the heart muscle. The tracer travels in the bloodstream and collects in areas of heart muscle that are receiving a good blood supply. The camera then captures images, comparing how the heart looks at rest with how it looks when it is working harder, or under “stress”. By placing the two sets of images side by side, the cardiologist can see whether particular areas of the heart are not getting enough blood, either all the time or only when the heart is pushed to work harder.
Why it is done
The main purpose is to investigate possible reduced blood flow caused by narrowed heart arteries. Your cardiologist may suggest it if you have chest pain, tightness or breathlessness that could be coming from the heart. It is also used to assess the extent of known heart disease, to check how the heart is coping after a previous problem, and sometimes to help plan before certain treatments or procedures. The results help your doctor decide whether further tests or treatment are needed.
How the “stress” is done
There are two ways to stress the heart. The first is physical exercise, usually walking on a treadmill or pedalling on a bike, with the pace gradually increased so the heart beats faster and works harder. The second option is for people who are unable to exercise, for example because of joint problems, mobility issues or breathing difficulty. In that case a medicine is given through a drip to mimic the effect of exercise on the heart’s blood flow. Your care team will decide which approach suits you before the test.
How to prepare
You will be given specific instructions beforehand, and it is important to follow them so the test works well. These usually cover food and drink, including avoiding caffeine, such as coffee, tea, cola, chocolate and some energy drinks, for a period before the test, because caffeine can interfere with the results. You may also be asked to pause certain heart medicines for a short time, but only do this if your doctor has told you to. Wear comfortable, loose clothing and suitable shoes in case you need to walk on the treadmill. If you have diabetes or take any regular medicines, ask the team in advance how to manage them on the day.
What happens during the test
A thin drip line is placed in a vein, usually in your arm, so the tracer can be given. A first set of resting images is taken to show blood flow while you are calm. Then the stress part begins, either through exercise or the medicine, while your heart rhythm, blood pressure and how you feel are closely monitored. Near the peak of stress, more tracer is given, and a further set of images is taken so the two states can be compared. The whole process takes some time and, at some centres, may be split over two visits or two parts of the same day, with rest between the resting and stress images.
What you might feel
During the exercise part you may notice a faster heartbeat, warmth, breathlessness, tiredness in the legs or brief chest discomfort, which is expected and closely watched. If the medicine is used instead, some people feel flushed, warm, slightly breathless, or notice a headache or a brief awareness of the heart beating. These sensations usually settle quickly once the test ends or the medicine is stopped, and the team is with you throughout. Tell the staff straight away if anything feels severe or worrying.
After the test
Once the images are complete, you can usually return to your normal activities, unless your doctor advises otherwise. You will be encouraged to drink plenty of fluids, which helps your body clear the tracer naturally through the urine over the following period. If any medicines were paused for the test, ask the team when to restart them. You can normally eat and drink as usual afterwards.
Results and next steps
Your cardiologist reviews the rest and stress images together. A normal result suggests blood is reaching the heart muscle well in both states. If an area shows reduced blood flow during stress but recovers at rest, it may point to a narrowed artery limiting blood supply when the heart works harder. An area that appears abnormal in both states may reflect older heart muscle damage. Depending on the findings, your doctor may recommend further tests, adjustments to medicines, lifestyle changes, or a procedure to improve blood flow. The results are always considered alongside your symptoms and other test findings.
Safety
The radiation dose from the tracer is small, and the test is carried out by trained staff who supervise you closely throughout. The stress part is monitored continuously, and the team can stop at any point if needed. Tell your doctor if you are pregnant, think you might be, or are breastfeeding, and mention any allergies or other medical conditions so the safest approach can be chosen for you.
When to seek help
A nuclear stress test looks into symptoms, but it is not a substitute for emergency care. Call 995 immediately if you have chest pain or tightness spreading to the arm, neck or jaw with sweating or breathlessness, or if you collapse. Do not wait for a scheduled test. After the test, seek medical advice promptly if you feel persistently unwell, notice ongoing chest discomfort, or have any reaction that concerns you.
Common questions
Is the radioactive tracer safe?
Yes. The tracer uses only a small amount of radioactive material and is generally considered safe for this test. It leaves your body naturally over time, and drinking fluids afterwards helps clear it. Let your doctor know if you are or might be pregnant, or are breastfeeding.
Do I have to exercise for the test?
Not necessarily. If you are able to walk on a treadmill or cycle, exercise is often preferred. If you cannot exercise, a medicine given through a drip is used instead to mimic the effect of exercise on your heart, so the test can still go ahead.
Why must I avoid caffeine beforehand?
Caffeine can interfere with how the stress part of the test works, particularly when the medicine is used, and may affect the results. Your team will tell you how long to avoid coffee, tea, cola, chocolate and similar items before your appointment.
Will the test tell me if I have blocked arteries?
It shows areas of the heart muscle that are not getting enough blood, which can suggest a narrowed artery. It does not directly picture the arteries themselves, so your cardiologist may recommend further tests to confirm the cause and guide treatment.
Can I drive and go back to work afterwards?
Most people return to normal activities the same day, unless told otherwise. If any medicines were paused or you feel unwell after the test, check with your care team before driving or resuming your usual routine.
Related guides
Sources
- National Heart Centre Singapore
- HealthHub
- NHS
- American Heart Association
Disclaimer: This guide is general information and not a substitute for advice from your own cardiologist or doctor. Always follow the specific instructions given by your care team. In an emergency, such as severe chest pain, breathlessness or collapse, call 995 immediately.