What Does Swelling In The Body Indicate?

My husband is a 58 year old male with type 2 diabetes that is controlled with insulin. 2 years ago he had valve replacement surgery (his first valve surgery he was 4 due to a premature birth) to replace the bottom right valve, repair the upper right valve and repair an unexpected hole. After change in our diet and continuous moderate exercise her began to slowly drop of excess weight and his enlarged heart slowly decreased size. 6 months later, still on our diet and exercise routine, he started to retain fluid and with it weight. Over the next year we went through every specialist our G.P. Could think of as our cardiologist insisted it wasn’t his heart. Each specialist tested and ruled out their field. We ended back with the cardiologist which (about a year later) found he had a fib but on the right side of the heart. Her was referred to a specialist that handles pediatric (as the valves were a pediatric problem) problems in adult bodies as well as adult issues. He did a liver biopsy to ensure he did not have cerosis of the liver ( he previously had hep C but went through the treatment and was cured) and found he only had slight fibrosis) and did an angiogram that showed a lot of presure In The heart. Thinking it might be constriction they did a cardiatric MRI and ruled it out.they admitted him into the hospital to give him IV lasix as the swelling on all his body due to water retention was so bad his legs would weep regardless of the compression socks he has worn for over a year. He has gained almost 50lbs of water retention in the past year, of which he has lost half of that while being in the hospital on IV. They have no answers to what is wrong with him or what is causing the excessive water retention