The electrocardiogram (ECG) is a test that checks for problems with the electrical activity of your heart. The heart’s electrical activity will be shown as line tracings on paper. This test effectively assesses your heart rhythm and is used to diagnose poor blood flow to the heart muscle (ischemia) and other abnormalities such as heart chamber enlargement and abnormal electrical conduction. It is one of the first tests to help determine if a heart attack is present. Even if there is no heart attack, the ECG can help decide whether any chest pain is due to angina (reduced blood flow to the heart muscle) or atherosclerosis (fatty deposits on inner walls of arteries).