Quick answer: a nuclear stress test (myocardial perfusion scan) compares pictures of blood flow to your heart muscle at rest and under stress, to look for blocked or narrowed coronary arteries. You get a small injection of radioactive tracer, rest images, then either exercise on a treadmill or bike or receive a medication that mimics exercise, a second injection and a second set of images. Avoid all caffeine, including decaf, for up to 48 hours before, and usually don’t eat after midnight. Each scan takes 15 to 30 minutes, but plan for 2 to 4 hours in the department.
Nuclear stress tests are a big part of nuclear medicine work. Most patients worry about the treadmill or about «something happening» during the stress part. The team monitors your heart the whole time, and the hardest part for most people is giving up their morning coffee.
What a nuclear stress test shows
The tracer travels with the blood into the heart muscle. Where blood flow is good, the muscle takes up plenty of tracer; where an artery is narrowed, less tracer arrives. Narrowing often only shows when the heart is working hard, which is why images at rest and under stress are compared.
Doctors use it to:
- investigate unexplained chest pain, chest pain with exercise (angina), shortness of breath on exertion or an abnormal ECG
- evaluate known or suspected coronary artery disease
- assess heart damage after a heart attack
- check results after bypass surgery or stents
- evaluate how well the heart pumps, using images synchronized with your ECG
How to prepare
- No caffeine for up to 48 hours, or as your center instructs. This includes regular and decaf coffee, hot and iced tea, caffeinated sodas, energy drinks, chocolate and medicines containing caffeine. Caffeine blocks the stress medication and can ruin the test.
- No smoking in the same period.
- Do not eat or drink after midnight, but you can usually take your medications with small sips of water unless told otherwise.
- Heart medications: if you take beta-blockers or calcium channel blockers, ask your doctor specifically whether to stop them temporarily. Do not stop on your own.
- Diabetes: ask your doctor for instructions for your diabetes medication on the day.
- Inhaler: if you use one for asthma or breathing problems, bring it and tell the team.
- Wear comfortable clothes and walking shoes. Don’t put lotion, oil or cream on your chest that day: the ECG stickers need to stick.
- Tell your doctor if you have had a recent heart attack, heart failure, asthma, chronic lung disease, heart rhythm or valve problems, or knee, hip or balance problems that make exercise difficult.
- Pregnancy and breastfeeding: always tell the team.
From the scanner room: [TU EXPERIENCIA: los errores de preparación más frecuentes (el café descafeinado, el chocolate, la crema en el pecho) y qué pasa si el paciente ha tomado cafeína.]
Step by step
1. The IV and the rest injection. A small IV is placed in your arm. The first dose of tracer is injected while you are at rest. You may feel a cold sensation in the arm.
2. Rest images. Within about an hour, you lie on the scanner table with your arms (or sometimes just your left arm) above your head for about 15 to 20 minutes while the camera takes pictures. The camera heads move close to your chest but do not touch you. Some scanners also take a short CT.
3. The stress test. ECG stickers are placed on your chest, and your blood pressure is checked regularly.
- Exercise: you walk on a treadmill or pedal a stationary bike, getting harder every few minutes, until you are too tired, short of breath, or have chest or leg pain, or until you reach the target heart rate. At peak exercise, the second tracer dose is injected.
- Medication instead: if you cannot exercise, you receive a drug that increases blood flow to the heart, like exercise does. It can cause a brief period of feeling anxious, dizzy, nauseous, shaky, short of breath or mild chest discomfort. These effects usually pass as soon as the infusion ends, and other medicines can be given to stop them if needed.
4. Stress images. You may be asked to drink some water, then lie on the table again for a second set of images, usually 15 to 30 minutes depending on the scanner.
From the scanner room: [TU EXPERIENCIA: cómo vive el paciente el esfuerzo farmacológico, qué le dices antes de empezar la infusión y cuánto tiempo pasa realmente entre las dos tandas de imágenes en tu servicio.]
How long does it take?
| Part | Typical time |
|---|---|
| Rest injection and waiting | Up to about an hour |
| Rest images | About 15 to 20 minutes |
| Stress test (exercise or medication) | A few minutes of exercise or infusion, plus preparation and recovery |
| Stress images | 15 to 30 minutes |
| Total time in the department | About 2 to 4 hours |
Some centers split the test over two days, with rest images one day and stress images another. Ask when you book.
After the test
Unless your doctor tells you otherwise, you can return to normal activities, including eating and, usually, your caffeine. Drink plenty of water to help flush out the tracer.
Is it safe?
The test uses a small dose of radiotracer, and allergic reactions are extremely rare. If you have coronary artery disease, you could have chest pain during exercise or the stress medication, but your heart is monitored throughout and medication can be given. Nuclear medicine tests have been used for more than six decades without known long-term harm from these low doses.
Understanding your results
A radiologist, nuclear medicine physician or cardiologist interprets the images and sends a report to your doctor. In general terms:
- Normal: good blood flow at rest and under stress.
- Reduced flow only under stress: suggests a narrowed artery that cannot supply enough blood when the heart works hard.
- Reduced flow at rest and under stress: may indicate scar tissue, for example from an old heart attack.
The report may also mention the ejection fraction, a measure of how well the heart pumps. Your doctor will explain what the results mean for your care; if a serious problem is found, further tests or treatment may follow quickly.
Tips from the technologist
[TU EXPERIENCIA: 3-4 consejos propios. Ideas: llevar comida para después de la prueba, zapatillas deportivas de verdad, avisar enseguida de cualquier síntoma en la cinta, no conducir si te has mareado.]
Frequently asked questions
Why can’t I have decaf before a nuclear stress test?
Decaf still contains some caffeine, which can block the stress medication and make the test inaccurate.
What if I can’t walk on a treadmill?
You will receive a medication that increases blood flow to the heart instead. You do not need to exercise.
Is a nuclear stress test painful?
No. Apart from the IV, the scans are painless. The exercise or medication can cause temporary discomfort, which the team monitors.
How long does a nuclear stress test take?
Usually 2 to 4 hours in the department, or two shorter visits if your center uses a two-day protocol.
Can I drive after a nuclear stress test?
Usually yes, unless you feel unwell. Ask the team before you leave.
This article is for general information and does not replace advice from your doctor or cardiology team. Do not stop heart medications without medical instructions.