Coumadin (Warfarin) is an oral anticoagulant that is currently used in cardiology and other fields of medicine to prevent or treat thromboembolic events (improper blood flow, clotting, and its effects). Some of these conditions include cerebrovascular accident (“stroke”), atrial fibrillation, blood clots in arteries or veins, pulmonary embolism, severe heart failure, extensive heart attacks, heart valve replacement, and sometimes, following stent placement in a blood vessel.