What Causes Swelling Of Elbow After Undergoing Heart Surgery For Valve Replacement?

Hi, my boyfriend has contracted endocarditis and ended up having to have open heart surgery to replace his valve 6 weeks ago. He has made a remarkable recovery, and has now finished his course of anti-biotics, and has been getting good feedback from his clinic visits/scans every 3 weeks. Since a few days ago though his elbow has become swollen, and has what feels like fluid around it - he cant remember if he has accidentally hit it off something. He said that he will go to the GP at the beginning of next week - I just wanted to check that it isnt something which should be checked out more urgently given his other recent medical conditions?