A stress test is a medical procedure that measures how well your heart works when it’s pumping hard. You walk on a treadmill (or receive a medication that mimics exercise) while a medical team monitors your heart rate, blood pressure, and electrical activity. The test is primarily used to detect coronary artery disease, evaluate chest pain, and assess how much physical activity your heart can safely handle.
Why Doctors Order a Stress Test
The most common reason is suspected coronary artery disease, where the arteries supplying blood to the heart become narrowed or blocked. At rest, even a partially blocked artery can deliver enough blood. But during exercise, the heart demands more oxygen, and a narrowed artery can’t keep up. A stress test forces that mismatch to reveal itself.
Your doctor might also order one if you have unexplained chest pain, new heart failure symptoms, a worsening of known heart disease, or a heart valve condition that needs evaluation before surgery. People who’ve had bypass surgery more than five years ago or a stent placed within the last two years are sometimes tested to check how well the repair is holding up.
What Happens During the Test
You’ll have electrodes placed on your chest to record an ECG (a tracing of your heart’s electrical activity), and a blood pressure cuff on your arm. The exercise portion typically lasts 10 to 15 minutes, though the full appointment, including setup and recovery, takes longer.
The most widely used format is the Bruce protocol. You start walking on a treadmill at a slow pace of about 1.7 miles per hour on a 10% incline. Every three minutes, the speed and incline increase simultaneously. The goal is to push your heart rate up to at least 85% of your age-predicted maximum, calculated with the simple formula: 220 minus your age. So for a 50-year-old, the target would be about 145 beats per minute. The test continues until you reach that target, develop symptoms, or can’t go any further.
After you stop exercising, a medical team monitors your heart rate, blood pressure, and ECG for about 15 minutes until everything returns to a normal range. Most people feel fine afterward, though some experience temporary fatigue.
When You Can’t Exercise: Pharmacological Stress Tests
If you can’t walk on a treadmill due to joint problems, lung disease, or other physical limitations, a medication can simulate the effect of exercise on your heart. The most commonly used drug today is regadenoson, approved by the FDA in 2008. It works by widening the coronary arteries, which increases blood flow to healthy vessels while revealing areas where blood flow is restricted by disease.
These medications don’t actually make your heart work harder the way exercise does. Instead, they create a detectable difference in blood flow between healthy and diseased arteries that shows up on imaging. A less common alternative, dobutamine, does directly increase the heart’s workload, more closely mimicking real exercise. It’s typically reserved for patients who can’t receive the standard vasodilator medications.
Types of Imaging Used
A basic stress test uses only the ECG to detect problems. It’s the simplest and fastest option, but it catches coronary artery disease about 68% of the time, with a specificity of 77%. That means it misses roughly a third of cases and occasionally flags a problem that isn’t there.
Adding imaging improves accuracy significantly. There are two main options:
- Stress echocardiography uses ultrasound to create real-time images of the heart before and immediately after exercise (or medication). It has a sensitivity of about 83% and specificity of 84% when paired with exercise, making it better at both catching disease and avoiding false alarms. It’s generally considered the most specific option, meaning fewer false positives.
- Nuclear perfusion imaging (SPECT) involves injecting a small amount of radioactive tracer into your bloodstream, then scanning the heart to see how blood flows through the muscle at rest and under stress. SPECT has a sensitivity of 82% and specificity of 76%. It’s considered slightly more sensitive than stress echo (better at catching disease) but less specific (more false positives). A newer version called PET scanning improves on both numbers, reaching 91% sensitivity and 89% specificity.
Tests that include imaging take longer. Expect to be in the stress lab for up to three hours for a nuclear or echo-based test, compared to roughly 30 to 45 minutes for a basic ECG-only version.
How Results Are Interpreted
Two things matter most: what the ECG shows and how long you were able to exercise.
On the ECG, doctors look at a specific segment of the heart rhythm tracing called the ST segment. If that segment drops by 1 millimeter or more in a flat or downward-sloping pattern during exercise, the test is considered abnormal, suggesting the heart isn’t getting enough blood. If the ST segment rises by more than 1 millimeter, that’s an even more serious finding that often leads to urgent follow-up testing. Results that fall in between are reported as equivocal, meaning unclear.
Exercise capacity is measured in METs (metabolic equivalents), where one MET equals the energy your body uses while sitting still. Reaching fewer than 5 METs is considered poor fitness, 5 to 8 is fair, 9 to 11 is good, and 12 or more is excellent. Your MET score is one of the strongest predictors of long-term cardiovascular health, independent of what the ECG shows. People with low exercise capacity face higher risk of heart problems even if nothing looks abnormal on the tracing.
How to Prepare
Preparation depends on which type of stress test you’re having. For nuclear or pharmacological stress tests, you’ll need to avoid all caffeine for 24 hours beforehand. That includes coffee, tea, cola, energy drinks, chocolate, and even decaffeinated versions, which contain trace amounts that can interfere with the medications used. You should also avoid eating, drinking, or smoking for at least three hours before your appointment.
Some medications may need to be paused before the test, particularly beta blockers (which slow the heart rate and can prevent you from reaching the target), diuretics, and nitrate medications. Don’t stop any medication on your own. Your doctor will tell you specifically which ones to hold and which to keep taking. If you take diabetes medications, ask for separate instructions about eating and dosing the morning of the test.
Wear comfortable walking shoes and loose clothing. The exercise portion isn’t a fitness test in the competitive sense. You’re not expected to run. The treadmill starts slowly, and the medical team is watching you closely the entire time.
What an Abnormal Result Means
An abnormal stress test doesn’t automatically mean you have a blocked artery. The basic ECG version, in particular, produces a fair number of false positives. If your results are abnormal or unclear, the next step is usually a more detailed imaging test, such as a CT angiogram or cardiac catheterization, to get a direct look at the coronary arteries. Your doctor will weigh the stress test findings alongside your symptoms, risk factors, and overall health before deciding on next steps.
A normal result is reassuring but not a guarantee. The test is best at detecting significant blockages, typically 70% or greater narrowing. Smaller plaques that could still cause problems years down the road may not produce detectable changes during exercise.