PT and INR are used to monitor the effectiveness of the anticoagulant warfarin (COUMADIN). This drug affects the function of the coagulation cascade and helps inhibit the formation of blood clots. It is prescribed on a long-term basis to people who have experienced recurrent inappropriate blood clotting. Common clinical indications for warfarin use are atrial fibrillation, the presence of artificial heart valves, deep venous thrombosis, and pulmonary embolism. Warfarin is also used in antiphospholipid syndrome, and occasionally in heart attacks. The goal with warfarin therapy is to maintain a balance between preventing clots and causing excessive bleeding. This balance requires careful monitoring, typically by PT/INR.