Dr Simon Kennon MB ChB, FRCP, MD Consultant Cardiologist

Treadmill Test

An exercise tolerance test (ETT) records the electrical activity of your heart whilst you exercise. It is used to diagnose ischaemic heart disease where the blood flow to the heart is reduced by a narrowing of the coronary arteries. This is a common cause of angina and other heart problems.

How is it done?

It usually involves walking on a treadmill or pedaling a stationary bike at increasing levels of difficulty.

Small electrodes are stuck on to your chest and the wires from the electrodes are connected to an electrocardiogram (ECG) machine.

The exercise starts at a very easy pace, and is gradually made more strenuous by increasing the speed and incline of the treadmill, or by putting some resistance on the bike wheel.

Whilst you exercise, ECG tracings are made and you will also have your blood pressure measured from time to time. The test lasts about 15-20 minutes.


An electrocardiogram (ECG) records the electrical activity of the heart. The heart produces tiny electrical impulses which spread through the heart muscle to make the heart contract. The machine amplifies the electrical impulses that occur at each heartbeat, and records them on to a paper or computer.

Many people with ischaemic heart disease have a normal ECG at rest. During exercise the heart beats faster and needs more oxygen. If one or more of your coronary arteries are narrowed, part or parts of the heart muscle do not get enough oxygen. This can cause the ECG tracing to become abnormal when you exercise. Therefore, if you have a positive ETT (an abnormal reading) you are likely to have ischaemic heart disease.

Limitations of the ETT

Whilst the ETT is valuable investigation, it is not 100% accurate. Sometimes tracings show changes during exercise, even though the person has a completely normal heart. Also, some people with ischaemic heart disease have a normal ETT with no changes on the tracing. Doctors are aware of this and use the results of the test in conjunction with other information such as your symptoms, results of other tests, etc.