My Husband Is 56 Yrs Old. He Had Open Heart

My husband is 56 yrs old. He had open heart surgery in 2008 on his aortic valve and was replace with a mechanical valve and has been on blood thinners. My husband is showing the same tiredness that he was showing before his valve replacement. My question is - can things go wrong with mechanical valves? I know your probably going to say check with his Dr. We will if you feel the need to do so. The Dr. is 360 miles from our hometown. Thank you.