My Mom had valve surgery, repaired about 3 weeks ago. She has been back in for several complications or for lack of better words fears. She had papltations which were really fast, we're dealing with those and controlling pressure. Then she had them again, went back to hospital and realized she needed some blood (for a second time) since surgery. She she got 2 units of blood and they gave her a shot in her stomach each day she was there (4 days) to make sure she didn't get any blood clots. She finally returned home and now she has dark brown urine...this has gone on for the last 3-4 days. She had blood taken and urine sample by her doctor, all results were negative. She had a sonogram today..doesn't look like anything abrnormal either. She is scheduled to see a Urologist on the 22nd of this month, of course she is worried. What could this possibly be a result of?