An exercise tolerance test is often requested to investigate the cause of chest pain or discomfort. The test will help determine if these symptoms are due to heart disease as there are many possible explanations for these symptoms. The test is also used to assess the effects of medications, your ability to exercise and to investigate abnormal heart rhythms and palpitations. An exercise tolerance test is an electrocardiogram (ECG) that is recorded while you are exercising, typically whilst walking or moving on a treadmill. This test will assess how well your heart works when you are active and your heart has to work harder. When you are active your heart requires more blood and oxygen. This test can show if there is a lack of blood through the arteries that supply the heart and can be carried out for people who complain of exercise-induced shortness of breath or chest pain too.