Cardiac arrhythmia can be harmless or in the other end of the spectrum, fatal. The most common long-term cardiac arrhythmia is atrial fibrillation (AF). It is the nasty one, because for some patients it causes symptoms, but many remain completely symptomless.
Regardless of the symptoms, the danger of atrial fibrillation is its increase in the risk of stroke casing 25% of the strokes. In fact, the first symptom of AF can be a large stroke with hemiplegia. Provided the atrial fibrillation is diagnosed before the stroke and proper anticoagulation therapy is initiated, approximately two thirds of AF-related strokes can be prevented.