Sometimes people who need valve surgery suffer from fluid retention because their hearts are not efficient at pumping. Then when they are in the hospital, they get pumped full of saline solution via IVs, since the saline solution is used as a vehicle for drugs.
Once home, it will take several weeks to a month to get rid of this type of fluid, and some may need diuretics.
I wouldn't rag on him too much for what may seem to be fat, it might not be, and may be beyond his control.
Please remember that his body is not operating in normal, optimum condition right now.
And fluid retention can accumulate in the extremities, but can also accumulate around the stomach area (ascites) causing a larger girth with rounded abdomen, tight waist bands, etc.