ECG telemonitoring is the application of single- or multichannel ECGs transmitted by telephone to the physician or an expert center. This enables the control of the health status despite the spatial separation of patient and physician. Cardiac arrhythmias, palpitations of unknown causes, the outcome of antiarrhythmic drug therapy or interventional ablation therapy can be diagnosed using ECG telemonitoring. Even asymptomatic arrhythmias, e.g. paroxysmal atrial fibrillation, may be detected. The use of a multichannel ECG facilitates the early prehospital diagnosis of an acute coronary syndrome and thus helps to optimize the chain of rescue. The telemonitoring of the ECG and additional physiological data enables the tele-care of patients with chronic heart failure. New types of implanted pacemaker or cardioverter/defibrillator devices allow telemonitoring of device data or ECG data for close control.