An Exercise Tolerance Test (ETT) measures how well the heart responds to physical activity. During the test, a patient typically walks on a treadmill or pedals a stationary bike while their heart rate, blood pressure, and electrocardiogram (ECG) are monitored. This helps doctors assess cardiovascular fitness and identify any potential heart problems. The ETT is often used to diagnose conditions like coronary artery disease or to evaluate the effectiveness of heart treatments. It can also help determine a safe level of exercise for patients recovering from heart issues. The test usually lasts about 10 to 15 minutes, depending on the individual's fitness level.