An electrocardiographic (ECG) scan can give an accurate picture of the heart’s function, showing the electrical activity of the heart in the form of curves drawn on a paper strip. It can be used to check the number of heart beats per minute, their regularity, the pacing and conduction of the heart, rhythm disturbances, myocardial oxygen deficiency and damage. Among many other conditions, it provides information on the size of the walls of the chambers that make up the heart, but also on the effects of the medicines used on heart function or their undesirable side effects. The test is particularly important for detecting cardiac arrhythmias, but many diseases (myocardial infarction, pericarditis, etc.) also cause characteristic ECG abnormalities. In many cases, the ECG signal only raises suspicion of certain diseases, which then need to be confirmed or ruled out by other tests. To diagnose cardiac arrhythmias, it is sometimes necessary to wear a portable ECG monitor (Holter) continuously for 24 hours or longer. Exercise ECGs are performed in suspected cases of a disease whose signs can only be detected by physical activity. The patient must then exercise on an exercise bike or treadmill during the test.