Event recorder monitoring plays an important role in the early detection and diagnosis of rhythm disorders such as atrial fibrillation (AF). In a recent study over 1000 patients with symptomatic paroxysmal AF were followed up by daily and symptom triggered ECG self monitoring. Independent of the presence of antiarrhythmic therapy, the incidence of AF was much higher than expected, since over 50% of AF episodes were asymptomatic. Therefore, patients symptoms are not a reliable surrogate parameter for the detection of AF. Moreover, antiarrhythmic therapy does not totally prevent atrial fibrillation, but raises the risk of silent AF episodes by reducing the mean heart rate. Based on these findings, effective anticoagulation should be taken into consideration in patients with paroxysmal AF independent of antiarrhythmic medication. The decision for anticoagulation with cumarine derivates or aspirin is dependent on the age, underlying diseases, and the individual thromboembolic risk in these patients.