Warfarin inhibits vitamin K dependent coagulation factors. It is used to thin the blood and is prescribed in the following conditions: heart arrhythmias (atrial fibrillation), stroke, heart stents, deep vein thrombosis (blood clot), pulmonary embolus (blood clot of the lung), mechanical heart valves, and hyper-coagulable disorders. The patient's blood is checked periodically to monitor the effectiveness of the medication. Dietary changes and new medications can alter the effects of the drug causing either too much or too little anti-coagulation.