I have afib so my doctor put me on warforin been on it for four month in November i had a very heavy period (ended up having a blood transfusion) it lasted over ten days. took me off the medication for a week then put me back on it and in December I had a strange period it lasted nine days but just spotted black blood. My periods are normally 5 days an average flow. I'm worried about the bleeding I know I need the blood thinners so I don't have a stroke. but the bleeding concerns me.