The factor V gene variant Leiden (FVL) and the prothrombin (factor II) gene variant G20210A (FIIV) are known risk factors for the development of venous thromboembolism13,14 and both have been studied regarding their effect on left atrial thrombogenesis in atrial fibrillation showing heterogeneous results (see Table 1). Here, F5 is linked to atrial fibrillation.