What is an ECG? — An ECG (also called an “electrocardiogram” or “EKG”) is a test that records a person’s heart rate (how fast it beats) and rhythm. It does this by measuring the electrical activity in the heart. A normal heartbeat happens when an electrical signal starts in a spot near the top of the heart. This signal follows a path to spread across the heart. As it spreads, the signal causes the heart muscle to squeeze. Each time the heart squeezes (“beats”), it pumps blood through the whole body.

What is a stress test? — A stress test measures how well the heart works when it is beating fast and working hard. When the heart pumps fast, it needs more blood. A stress test helps doctors see if the heart is getting enough blood during these times. A stress test is sometimes called an “exercise test” or a “treadmill test.”

A person can have an ECG without having a stress test. But if a person has a stress test, he or she will always have an ECG with it.

Why might my doctor order an ECG or a stress test? — Your doctor might order an ECG to:

  • See if you are having or had a heart attack
  • Look for other heart conditions or follow a known heart condition
  • Help figure out why you have chest pain, trouble breathing, dizziness, a fast heart rate, or other symptoms
  • Check how healthy your heart is before you have surgery
  • Check how well your heart medicines or other heart treatments are working

Doctors usually order stress tests to check for problems that can happen when the heart works hard. Your doctor might order a stress test to:

  • See if you have coronary heart disease, heart failure, or another heart condition – Coronary heart disease is a condition that puts you at risk for a heart attack and other types of heart disease. Some people have symptoms of coronary heart disease only when they exercise. Heart failure is a condition in which the heart doesn’t pump well.
  • Check how well your heart works after heart surgery
  • Help figure out why you have chest pain, trouble breathing, or other symptoms
  • See if you can safely exercise after a heart attack

How do I prepare for an ECG or a stress test? — Before an ECG, you don’t need do anything special. But you should tell your doctor what medicines you take, because they might affect the test results.

To prepare for a stress test, you will probably need to avoid eating, drinking, or smoking for 3 hours beforehand. If you are on any heart medicines, you might also need to change or stop some of them before the test. Your doctor or nurse should tell you if you need to change or stop any of your medicines.

For your stress test, you should wear comfortable clothes that you can exercise in. You should also bring any inhalers that you use to help your breathing.

What happens during an ECG and stress test? — For an ECG, a doctor, nurse, or technician will first stick patches (called “electrodes”) onto your chest, arms, and legs (figure 1). Wires connect the patches to the ECG machine. The machine will measure and record your heart’s electrical activity and print out the results. Having an ECG doesn’t hurt.

For a stress test, the doctor, nurse, or technician will first do an ECG and measure your blood pressure. Then he or she will “stress” your heart and increase your heart rate by doing one of the following things:

  • Have you run or walk on a treadmill (figure 2)
  • Have you pedal a stationary bike (a bike that doesn’t move, except for the pedals)
  • Give you medicine to make your heart beat faster – People who can’t run or walk can get medicine instead of exercising.

Sometimes, doctors do imaging tests during a stress test. These kinds of tests can create images of the blood flow to the heart.

During your stress test, the doctor or nurse will watch you. He or she will check your blood pressure, do several ECGs, and ask how you feel. You might also need to breathe into a tube at certain times during the test. The test will end when you can’t exercise anymore or when your doctor or nurse tells you the test is over.