A 24-year-old male patient came to the emergency room with melena, gum bleeding and nosebleeds. This patient has a history of mechanical prosthetic mitral valve replacement for severe mitral regurgitation (MR) and consumed warfarin irregularly, but did not come back for regular check-up. Investigations showed greatly increased thyroid function and international normalised ratio (INR) was 15.8. Patients were diagnosed with thyroid storm and bleeding due to prolongation of INR. His hyperthyroid state might have caused increased rate of degradation of vitamin K-dependent clotting factor thereby increased sensitivity to warfarin. Concomitant acute decompensated heart failure, thrombocytopenia and hypoalbuminemia also contributed to his risk of bleeding. Treatment included anti-thyroid therapy as well as warfarin reversal therapy by stopping warfarin, low-dose intravenous vitamin K due to his mechanical …