Many people who suffer from irregular heartbeats (atrial fibrillation) which might cause stroke, need to take blood thinners to prevent it. However, people with atrial fibrillation are also at increased risk of acute myocardial infarction or unstable angina pectoris (another heart condition marked by a chest pain, comprising so-called acute coronary syndrome for which another type of treatment that prevents blood from clotting (antiplatelet treatment) is indicated. In particularly if such patients undergo percutaneous coronary intervention, a procedure aimed to open up diseased blood vessels and hence to treat acute coronary syndrome, this treatment is needed. If a patients takes several anti-clotting blood drugs, the risk of bleeding is high. The number of possible drug combinations and treatment durations is large. This study will help us to understand which anti-clotting drug combinations are prescribed in real life among patients with atrial fibrillation and acute coronary syndrome, how effective and safe they are for patients. The study will look into the data that are already available in several very large Swedish databases which contain information needed for the research.