Computer-supported long-term ECG-analysis, must be considered as complementary to other methods of documentation concerning arrhythmias. With the introduction of computers in the last several years, exact quantification and qualification of arrhythmias, over long monitoring periods, has become possible. With this method diverse forms of documentation and data presentation enhance its value of information and increase plausibility. Major indications for long-term ECG-monitoring of ambulatory patients are detection of occult arrhythmias, evaluation of subjective symptoms such as dizziness or syncope, recognition of pacemaker dysfunctions, selection of patients with coronary heart disease at high risk and evaluation as well as control of the efficacy of antiarrhythmic therapy.