In a stress test, you exercise or run and walk on a treadmill which makes your heart work progressively harder.

Abnormalities in blood pressure, heart rate, or ECG or worsening physical symptoms could point to coronary artery disease (CAD). 

When do you need an ECG/ECG Stress Test?

if you have symptoms of heart disease, such as chest pain, shortness of breath, an irregular heartbeat, or heavy heartbeats. You may also need the tests if you have a history of heart disease. And you may need these tests if you have diabetes or other risks.