Electrocardiography (ECG) has great importance in the diagnosis of cardiac arrhythmias, acute myocardial infarction and many other heart diseases. This is a method of recording electrical activity of the heart through electrodes placed on the patient's skin. By capturing the electrical activity of the heart, a technical record called an electrocardiogram is produced. In the conduction system of the heart it is important to emphasize four structures – sinoatrial node, atrioventricular node, bundle of His and Purkinje's fibers. If function of one structure fails, heart rate disorders occur. There are several ways to performe ECG. The most commonly used method is 12-leads electrocardiography. The remaining methods are continuous electrocardiography (Holter), telemetry and permanent ECG monitoring by transtelephone or loop recoders. On the ECG record it is important to know its parts (waves, intervals, segments) which helps in spotting ECG abnormalities. Parts that are useful to know are P wave, QRS complex, T wave, ST segment, U wave, QT interval and PQ interval. The importance of knowing the ECG for a physiotherapist is most commonly see in performing ergometry. During ergometry, physiotherapist plays a major role and is responsible for recognizing an abnormal ECG finding.