The 12-lead resting surface ECG plays a major role in the diagnosis of cardiac arrhythmias. As a screening method, it provides important information about the cardiac rhythm and possible underlying heart diseases. It enables interpretation of possible arrhythmia mechanisms, especially if the recording is obtained at the time of the rhythm disorder. Since rhythm disorders exhibit spontaneous variability, event recorders and Holter monitoring are very helpful complementary noninvasive tools in the diagnosis of cardiac arrhythmias. In addition, Holter ECG can be used in monitoring the response to antiarrhythmic agents and in risk stratification of arrhythmias in certain cardiac disease states. Physical exercise, by inducing physiological and pathophysiological changes, may provoke arrhythmias, which forms the basis of exercise-stress testing. Stress testing may also be indicated when antiarrhythmic agents are initiated or therapy altered. Electrophysiological Study (EPS) is a time-consuming and costly investigation, which in general is reserved for further evaluation of tachyarrhythmias, conduction disturbances and syncope of unknown origin and routinely performed prior to radiofrequency ablation. EPS should only be performed in tertiary-care centers by well-trained and experienced cardiac electrophysiologists.