How a Stress Test Works

A cardiac stress test — also called an exercise stress test, exercise tolerance test (ETT), or treadmill test — is a diagnostic procedure that evaluates how the heart responds to physical exertion. By progressively increasing exercise workload while continuously monitoring the ECG and vital signs, the stress test can reveal coronary artery disease that may not be apparent at rest, assess functional capacity, evaluate symptoms like chest pain or shortness of breath, and gauge a patient's cardiovascular fitness and prognosis.

Why Stress Is Needed To Detect Coronary Artery Disease

Coronary artery disease (CAD) causes narrowing of the coronary arteries. At rest, blood flow through a narrowed artery may be adequate — the heart muscle receives enough oxygen for its resting metabolic needs. The narrowing only becomes problematic when demand increases. During exercise, the heart works significantly harder: heart rate and contractility increase substantially, and myocardial oxygen demand rises 5–10 times above resting levels.

If a coronary artery is narrowed by 70% or more, the increased blood flow required during exercise cannot be delivered — the heart muscle becomes ischemic (deprived of oxygen). Ischemia produces characteristic changes on the ECG (ST segment depression), may cause chest pain (angina), and may produce abnormal wall motion visible on echocardiography or perfusion defects visible on nuclear imaging.