Patients with a bioprosthetic mitral valve are prescribed anticoagulants, such as warfarin, for 6 weeks to 3 months after their operation, while patients with mechanical valves are prescribed anticoagulants for the rest of their lives. Anticoagulants are taken to prevent blood clots, which can move to other parts of the body and cause serious medical problems, such as a heart attack. Anticoagulants will not dissolve a blood clot but they do prevent other clots from forming or prevent clots from becoming larger.