ACENOCOUMAROL is prescribed to prevent unwanted clots from forming if you have a condition that puts you at risk of this happening, such as atrial fibrillation, or if you have had a heart valve replacement. It is also given to prevent any clots that may have already formed in the blood vessels of your legs, lungs or heart from becoming larger and causing problems. ACENOCOUMAROL works by increasing the time it takes for your blood to clot, reducing the risk of a stroke or heart attack. This medication helps to keep blood flowing smoothly in your body by decreasing the amount/number of clotting proteins in the blood. ACENOCOUMAROL does not dissolve blood clots that have already formed but may stop them from becoming larger and causing more serious problems.